Port the fishing rods and wild Magikarp

The Old, Good and Super Rods run FishFunction facing water: the map's fish
group and Fish pick no fish, no bite, or a Pokémon from FishGroups and the
time of day's TimeFishGroups. The player casts and jiggles with the
fishing frames drawn from LoadFishingGFX's tiles, shows "!" on a bite, and
the hooked Pokémon attacks as BATTLETYPE_FISH. Facing pieces now use
signed offsets, which the rod above and left of the player needs.

Wild Magikarp no longer stop a battle: LoadEnemyMon redraws their DVs
through CalcMagikarpLength and its filters, as the original does. The
length routine matches the original in the reference emulator.

Part of #27

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

src/game/scripts/start-menu.ts

@@ -111,6 +111,8 @@ export type MenuFieldMove =
       wild?: { species: number; level: number };
       /** hLastTalked, when the move acts on a facing object. */
       lastTalked?: number;
+      /** BATTLETYPE_FISH: the wild Pokémon is on a fishing rod's hook. */
+      fish?: boolean;
     }
   | { texts: number[] }
   | { notice: string }
@@ -144,6 +146,8 @@ export interface StartMenuHost {
   gameTime(): GameTime;
   /** CheckForHiddenItems: an unfound hidden item on the screen. */
   hiddenItemOnScreen(state: ScriptState): boolean;
+  /** FishFunction with rod 0-2: a script, or a silent failure. */
+  fish(state: ScriptState, rod: number): MenuFieldMove;
 }
 
 /** The overworld start menu (engine/menus/start_menu.asm) with its
@@ -989,6 +993,20 @@ export class StartMenuRun {
         this.deferred = MENU.SacredAshScript;
         this.deferredItem = item;
         return true;
+      case MENU.OldRodEffect:
+      case MENU.GoodRodEffect:
+      case MENU.SuperRodEffect: {
+        // UseRod: FishFunction queues a script unless it fails.
+        const result = this.host.fish(
+          this.state,
+          effect === MENU.OldRodEffect ? 0 : effect === MENU.GoodRodEffect ? 1 : 2,
+        );
+        if (!("script" in result)) return false;
+        this.deferred = result.script;
+        this.deferredItem = item;
+        this.deferredMove = result;
+        return true;
+      }
       case MENU.ItemfinderEffect:
         // ItemFinder: one script or the other, and always a success.
         this.deferred = this.host.hiddenItemOnScreen(this.state)