Open Route 30 with map trainers and multi-Pokémon trainer battles

Map trainers run the ROM's TalkToTrainerScript and SeenByTrainerScript.
_CheckTrainerBattle runs before tile events at the end of each step and
on idle ticks; TrainerWalkToPlayer builds wMovementBuffer natively, and
writeobjectxy keeps the trainer where it stopped. The interpreter gains
the trainer header commands, wRunningTrainerBattleScript and hidden
items (HiddenItemScript).

Trainers with several Pokémon send out the next one through
EnemyPartyMonEntrance and FindMonInOTPartyToSwitchIntoBattle, including
its BattleRandom fallback. AI_SwitchOrTryItem, CheckAbleToSwitch and
AI_Switch are translated with their original bugs, and wPlayerUsedMoves
is recorded. The Shift-mode switch offer, trainer items, Pursuit on a
switch, Perish Song and Spikes remain refused.

Route 30 and its Berry house are enabled; Mr. Pokémon's house and
Route 31 stay closed. A refused trainer sighting does not restart until
the player moves, so a rollback cannot trap the player in view.

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

README.md

@@ -2,13 +2,15 @@
 
 A native web port of Pokémon Crystal, translated from [PRET's Game Boy disassembly](https://github.com/pret/pokecrystal). The game runs in TypeScript and reads graphics, maps, sprites and dialogue from the user's own ROM. No original game assets are included.
 
-**Current milestone: from the opening to Cherrygrove City.** Play in a minimal Crystal-style interface with Game, Savegames, Map, Pokédex, Link and Friends tabs. The native canvas fills the play area, and the live local map follows your position. Save, export and import work now. Pokédex, Link and Friends show their planned scope without placeholder data.
+**Current milestone: from the opening to Route 30.** Play in a minimal Crystal-style interface with Game, Savegames, Map, Pokédex, Link and Friends tabs. The native canvas fills the play area, and the live local map follows your position. Save, export and import work now. Pokédex, Link and Friends show their planned scope without placeholder data.
 
 Walk around your home, the town and its buildings at the original walking speed. Mom gives you the Pokégear and asks the day of the week. The teacher stops you from leaving town. Your rival shoves you away from the lab window. Professor Elm introduces his errand, and you choose Chikorita, Cyndaquil or Totodile. The Pokémon's picture and stats come from your ROM, and you can nickname it. Elm's aide then gives you a Potion. These scenes run the game's own event scripts and movement data, with native choices and naming.
 
 With a Pokémon, head west along Route 29 to Cherrygrove City. Wild Pokémon appear in the grass and battle you with their original moves. The route has ledges, signs, an item ball and a Berry tree that regrows daily. Townspeople wander and look around as in the original. In Cherrygrove, the Guide Gent gives a tour, the Poké Mart buys and sells items, the Pokémon Center nurse heals your party, and a whiteout returns you to the last Pokémon Center you entered.
 
-Catching, trainer battles, Route 30 and beyond, party and bag menus, decorations and audio are still being ported. Unported neighboring areas appear at the edges but cannot be entered yet.
+North of Cherrygrove, Route 30's trainers battle you. Bug Catcher Don spots you from a distance and walks over; Youngster Mikey battles when you talk to him. Each sends out two Pokémon, and beaten trainers remember you. The Berry house gives a Berry, and a Potion is hidden on the route.
+
+Catching, Mr. Pokémon's house and the Mystery Egg errand, Route 31 and beyond, party and bag menus, decorations and audio are still being ported. Unported neighboring areas appear at the edges but cannot be entered yet.
 
 ## Run