Port MAIL in the party menu and the PC's MAIL BOX

Giving MAIL opens the mail entry: two lines of up to sixteen characters,
kept with the player's name and ID, the holder's species and the MAIL.
The party submenu's MAIL reads the letter or takes it, either to the PC's
MAILBOX (ten at most) or into the pack without its message. The player's
PC lists the MAILBOX by author to read, put in the pack or attach, and
Bill's PC keeps a Pokémon holding MAIL out of the boxes. Saves keep each
holder's MAIL and the MAILBOX.

The letter shows its message and author natively; the stationery's
graphics are not drawn yet.

Closes #27

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/PLAN.md

@@ -125,7 +125,7 @@ The numbered sections below keep their full scope. Each one opens with a checkli
 - `TileCollisionStdScripts` is read from the ROM, so facing a `COLL_PC` tile (in any direction, as in the original) runs `PCScript`. Bookshelves, TVs and similar tiles no longer need the player to face up.
 - `PokemonCenterPC` checks for a Pokémon, then lists the PCs from `PokemonCenterPC.WhichPC`: Bill's PC and the player's PC, plus Oak's PC once the Pokédex is owned. The Hall of Fame PC is refused, since no Hall of Fame entry can exist yet.
 - Bill's PC: deposit (`BillsPC_CheckMail_PreventBlackout` keeps the last Pokémon and the last one that has not fainted; `RestorePPOfDepositedPokemon`), withdraw (`CalcLevel`, then `CalcMonStats` with stat experience, full HP and no status), release with confirmation ("Bye," with the species name), and change box: switch with the ROM's confirmation, name (a blank name keeps the old one) and print (only the empty-box message). Menus and messages come from the ROM; lists are presented natively with each Pokémon's level or each box's count.
-- The player's PC withdraws, deposits (from every pocket; untossable items move one at a time) and tosses items (up to 50 stacks, `RemoveItemFromPocket` slot rules), and shows the empty mail box. The house PC adds DECORATION, which closes the PC after a change.
+- The player's PC withdraws, deposits (from every pocket; untossable items move one at a time) and tosses items (up to 50 stacks, `RemoveItemFromPocket` slot rules), and holds MAIL since the remaining field items section. The house PC adds DECORATION, which closes the PC after a change.
 - Oak's PC rates the Pokédex from `OakRatings`.
 - Capture with a full party runs `SendMonIntoBox`: the Pokémon goes first in the current box, with restored PP and `SetBoxMonCaughtData`, can be nicknamed and shows `BallSentToPCText`. If the box is already full the ball is not used (`Ball_BoxIsFullMessage`). A catch that fills the box sets `BATTLERESULT_BOX_FULL`; `reloadmapafterbattle` then queues Bill's call (`Script_SpecialBillCall`) as a memory script that runs at the next `PlayerEvents` and is not saved, as in the original.
 - `VAR_BOXSPACE` reads the current box.
@@ -169,7 +169,7 @@ The numbered sections below keep their full scope. Each one opens with a checkli
 - PACK: the Items, Balls, Key and TM pockets (left and right change pockets; there are no TMs or HMs yet), and each item's submenu chosen by its permissions and field menu (`USE`, `GIVE`, `TOSS`, `SEL`, `QUIT`). TOSS asks how many and confirms. USE follows `UseItem`: Oak's warning without a field use, "You don't have a POKéMON!" for party items without one, and `_DoItemEffect` by the item's `ItemEffects` address: Potions and the other `HealingHPAmounts` items, status healers, Full Restore, Revive and Max Revive, the bitter Energypowder, Energy Root, Heal Powder and Revival Herb, Ethers, Elixers, the MysteryBerry and PP Up. The Bicycle closes the menu and runs `Script_GetOnBike` or `Script_GetOffBike` outdoors; elsewhere Oak objects, because `wFieldMoveSucceeded` shares `wItemEffectSucceeded`'s byte.
 - PP Up keeps a quirk: `wUsePPUp` shares `wTempPP`'s byte, so `ComputeMaxPP` adds one step (a fifth of the base PP, at most 7) to the current PP as well as the maximum. Sketch and moves with three PP Ups are "maxed out".
 - The menu runs on a script draft, like the PC. Changes commit when it closes; a save made while it is open keeps the state from before it. The start menu cursor, the party menu cursor and the last pocket stay in memory between openings and are cleared after a battle, as `CleanUpBattleRAM` does. The party cursor reaches the next battle's `ChangeHappiness`.
-- Not ported: MAIL (it gives a notice and changes nothing). The Escape Rope runs since the Fly section below; Repels and the other field items, the rods, item reordering with Select and left and right on the MOVE screen since the last section. Rare Candy, evolution stones and vitamins run since the evolution section below; field moves, SEL and Select since the section after it.
+- The Escape Rope runs since the Fly section below; Repels and the other field items, the rods, item reordering with Select, left and right on the MOVE screen and MAIL since the last section. Rare Candy, evolution stones and vitamins run since the evolution section below; field moves, SEL and Select since the section after it.
 
 ## Implemented: evolution
 
@@ -251,6 +251,7 @@ The numbered sections below keep their full scope. Each one opens with a checkli
 - The Old, Good and Super Rods fish facing water, never while surfing (Oak objects otherwise; the facing tile may hold an object, as in the original). The map header's fish group decides: none gives "Not even a nibble!" at once; otherwise `Fish` bites below 50% + 1 and picks the rod's `FishGroups` entry, with `TimeFishGroups` for the morning and day or the night. The player casts with the fishing frames (`LoadFishingGFX`'s body and rod tiles), jiggles four times on a bite, shows "!", and after "Oh! A bite!" puts the rod away before a `BATTLETYPE_FISH` battle: "The hooked MAGIKARP attacked!". Qwilfish and Remoraid swarms come from trainer calls, which are not ported. New Bark Town, Route 30 and Cherrygrove City have fish.
 - In the start menu's pack, Select marks an item and asks "Where should this be moved to?"; A or Select on another row of the same pocket moves it there (the rows between shift), merging it into a stack of the same item unless either holds 99 (what exceeds 99 stays behind), and B ends the move without leaving the pack. Left and right keep the pocket meanwhile. The packs that GIVE and the PC open ignore Select, as `DepositSellPack` does.
 - On the MOVE screen, left and right show the previous or next party member's moves, skipping Eggs (`MoveScreenLoop`'s `.cycle_left` and `.cycle_right`, which come back to the same Pokémon past either end), with the cursor back on the first move; not while a move is being moved. The party menu's cursor follows.
+- MAIL: giving MAIL (from the pack, or swapped for a held item) opens the mail entry, two lines of up to 16 characters with the second after a full first one (`_ComposeMailMessage`), and keeps the message with the player's name and ID, the holder's species and the MAIL (`ComposeMailMessage`). A Pokémon holding MAIL shows MAIL in its submenu: READ shows the letter (the message and the author; the stationery's graphics are not drawn yet), TAKE asks "Send the removed MAIL to your PC?" (`SendMailToPC`: up to ten in the MAILBOX, else "Your PC's MAILBOX is full."), or on NO "The MAIL will lose its message. OK?" and puts the item in the pack. SWITCH carries the MAIL with its Pokémon; another item still needs "Please remove the MAIL first."; Bill's PC refuses to deposit or release a Pokémon holding MAIL ("Remove MAIL."). The player's PC MAIL BOX lists the MAIL by author with READ MAIL, PUT IN PACK (the message is lost) and ATTACH MAIL (not to an Egg or a Pokémon holding an item). The mail entry offers the original's characters that have one of their own; `<PK>`, `<MN>`, `<PO>`, `<KE>` and the 'd-'v ligatures are left out. Save format 3 gained each Pokémon's `mail` and the `mailbox`, migrated by absence to none.
 - Wild Magikarp now battle: `LoadEnemyMon` draws their DVs again as the original does, through `CalcMagikarpLength` (compared with the original routine) and its filters, whose millimetre limits only work as a floor of four feet that about 39% of draws skip (39 percent + 1), nowhere in map group 9 or on maps numbered 6 (the Lake of Rage check). Unown are still refused.
 - Save format 3 gained `repel`, `coins` and `blueCardBalance`, migrated by absence to 0.
 
@@ -336,7 +337,7 @@ Introduce native player, party, Pokémon, inventory, money and quest models. Rea
 
 Expand script calls, choices, scene state, inventory commands and native special handlers. Translate routines reached through assembly calls into explicit native services; never fall back to emulator execution in the shipping game.
 
-Meeting Mom, Elm's introduction, the starter, the aide's Potion, Route 29, Cherrygrove, Route 30's trainers, Mr. Pokémon's house, the Cherrygrove rival battle, the return to Elm, capture, the catching tutorial, the PC, the introduction's naming and clock screens, and switching and healing items in battle run now. The opening milestone is complete within the recorded acceptance boundaries. The start menu, party menu and pack now run outside battle, and Pokémon evolve. Field moves from the menu, SEL/Select and MOVE PKMN W/O MAIL run too, and the Pokégear's clock, map and phone cards, with calls to Mom and Elm, Mom's bank at home and her purchases, the trainer card with the play time, the options, Fly, Dig, Teleport and the Escape Rope, and Headbutt and Rock Smash with their encounters. Next: the remaining field items, MAIL and pack reordering.
+Meeting Mom, Elm's introduction, the starter, the aide's Potion, Route 29, Cherrygrove, Route 30's trainers, Mr. Pokémon's house, the Cherrygrove rival battle, the return to Elm, capture, the catching tutorial, the PC, the introduction's naming and clock screens, and switching and healing items in battle run now. The opening milestone is complete within the recorded acceptance boundaries. The start menu, party menu and pack now run outside battle, and Pokémon evolve. Field moves from the menu, SEL/Select and MOVE PKMN W/O MAIL run too, and the Pokégear's clock, map and phone cards, with calls to Mom and Elm, Mom's bank at home and her purchases, the trainer card with the play time, the options, Fly, Dig, Teleport and the Escape Rope, and Headbutt and Rock Smash with their encounters, every remaining field item, the fishing rods, MAIL, moving items with Select and the MOVE screen's other Pokémon. Next: the remaining battle commands, move effects and Smart AI handlers (board #28).
 
 Complete and validate the native battle engine: deterministic randomness, stats, move selection, accuracy/critical checks, damage, status, turn order, switching, fainting, experience, capture and rewards. Compare controlled seeds and states with the original, including integer rounding and overflow behavior.