Port the start menu, the party menu and the pack outside battle

Start opens the original start menu. POKéMON shows the party with the
Pokémon submenu (stats, switching, move order, held items); PACK shows the
four pockets with the field item effects for healing, PP and the Bicycle,
plus giving and tossing. The menu runs on a script draft, and its cursors
persist until a battle clears them. Select keeps the Key Items shortcut.

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

docs/ARCHITECTURE.md

@@ -56,8 +56,13 @@ state in version-3 saves, with defaults for older saves. Forced terrain and
 turn-in-place timing run through the idle movement path. Dynamic warps and
 elevators retain their return destination. Block mutations use a per-map working
 copy and a revision counter, so rollback and the minimap see the same terrain.
-Surf, Cut and Strength use the ROM scripts. Start/Select opens the Key Items
-menu, pausing overworld ticks while choosing the Bicycle. The bedroom PC edits
+Surf, Cut and Strength use the ROM scripts. Select opens the Key Items
+menu, pausing overworld ticks while choosing the Bicycle. Start opens
+`scripts/start-menu.ts`, a native run on a script draft like the introduction:
+the party menu and pack change only the draft, which commits when the menu
+closes, and an item that queues a script (the Bicycle) starts it afterwards.
+The start menu, party menu and pocket cursors live in the world's memory,
+not in saves, and are cleared after each battle. The bedroom PC edits
 decorations on the script draft and reloads the room when the menu commits.
 `scripts/intro.ts` runs a new game's introduction as a native generator on a
 script draft; the session starts it only when nothing is saved, and the name,