feat(yellow): port SurfingPikachu behaviour

Yellow's IsSurfingPikachuInParty swaps the player's overworld sheet to
a Pikachu-on-a-surfboard when the party mon that knows SURF is a
Pikachu. The recomp was missing both halves of this: the sheet was
never extracted, and the engine had no seam for the swap.

Extraction: SurfingPikachuSprite (gfx/sprites/surfing_pikachu.2bpp)
loads outside SpriteSheetPointerTable via
LoadSurfingPlayerSpriteGraphics2, the same bypass RedBikeSprite uses.
Added the symbol to the Yellow manifest and a parallel extract in
RomExtractor / build_rom_data / extract/sprites, minting
SPRITE_SURFING_PIKACHU. PaletteFX colors it (player OBP palette, same
as the bike).

Engine: new field.playerSprites.surfPikachu (default
SPRITE_SURFING_PIKACHU, guarded so before extraction the ride keeps
the Seel). Player.new caches surfPikachuSprite; pose() picks it when
surfing and the SURF-mon is a Pikachu. New
OverworldState:syncSurfingPikachu derives the flag from partyKnows at
every surf-state toggle (mount, dismount, fly, teleport, blackout,
forced-surf tile, boot-restore). Runtime-only, re-derived at load so a
party change between save and load is honored.

Lane B: RFC at docs/rfcs/0001-surfing-pikachu-sprite.md.
Backward-compatible — existing mods see no change (surf still defaults
to SPRITE_SEEL; surfPikachu only resolves on a Yellow import after
regeneration). Parity tests in tests/parity_surfing_pikachu_sprite.lua
(12/12) and tests/mod_world_tests.lua (19229/19229 with the new
boot-seed checks). tests/parity_cinnabar_east_surf.lua (24/24)
unchanged.

Regeneration required: re-run make_yellow_manifest.py against a
pret/pokeyellow checkout, then re-import the Yellow ROM.

tools/build_rom_data.py

@@ -461,6 +461,27 @@ def extract_sprites(rom, symbols, manifest, out_dir, assets_dir):
         "walker": bike_frames >= 6,
     }
 
+    # Yellow-only: the surfing-Pikachu overworld ride sheet, loaded
+    # outside SpriteSheetPointerTable (LoadSurfingPlayerSpriteGraphics2) --
+    # same extra extract as RedBikeSprite. (RFC 0001)
+    surf = manifest["sprites"].get("surfPikachu")
+    if surf and _has_symbol(symbols, surf["label"]):
+        surf_symbol = _symbol(symbols, surf["label"])
+        surf_length = surf["imageWidth"] * surf["imageHeight"] // 4
+        _write_2bpp_png(
+            rom.bytes(surf_symbol.bank, surf_symbol.address, surf_length),
+            surf["imageWidth"], surf["imageHeight"],
+            os.path.join(assets_dir, "sprites", surf["imageBase"] + ".png"),
+            transparent_color0=True)
+        surf_frames = surf["imageHeight"] // 16
+        out["SPRITE_SURFING_PIKACHU"] = {
+            "id": "SPRITE_SURFING_PIKACHU",
+            "source": f"ROM:{surf['label']}",
+            "image": f"assets/generated/sprites/{surf['imageBase']}.png",
+            "frames": surf_frames,
+            "walker": surf_frames >= 6,
+        }
+
     util.write_lua(
         os.path.join(out_dir, "sprites.lua"), out,
         header="Source: canonical Pokemon Red ROM (overworld sprite sheets)")

tools/extract/sprites.py

@@ -83,6 +83,23 @@ def extract(pokered, out_dir, assets_dir, sprite_order):
             "walker": frames >= 6,
         }
 
+    # Yellow-only: the surfing-Pikachu overworld ride sheet, loaded
+    # outside SpriteSheetPointerTable (LoadSurfingPlayerSpriteGraphics2) --
+    # same extra extract as RedBikeSprite. (RFC 0001)
+    surf_src = files.get("SurfingPikachuSprite")
+    if surf_src:
+        png_src = os.path.join(pokered, re.sub(r"\.2bpp$", ".png", surf_src))
+        dst = os.path.join(assets_dir, "sprites", "surfing_pikachu.png")
+        size = gfx.convert_png(png_src, dst, transparent_color0=True)
+        frames = size[1] // 16
+        out["SPRITE_SURFING_PIKACHU"] = {
+            "id": "SPRITE_SURFING_PIKACHU",
+            "source": "gfx/sprites.asm SurfingPikachuSprite (LoadSurfingPlayerSpriteGraphics2)",
+            "image": "assets/generated/sprites/surfing_pikachu.png",
+            "frames": frames,
+            "walker": frames >= 6,
+        }
+
     util.write_lua(os.path.join(out_dir, "sprites.lua"), out,
                    header="Sources: data/sprites/sprites.asm, gfx/sprites/*.png\n"
                           "Frame order (walker): stand D/U/L, walk D/U/L; right = flipped left.")

tools/make_rom_manifest.py

@@ -280,7 +280,7 @@ def sprite_metadata(pokered, order):
     bike_png = re.sub(r"\.2bpp$", ".png", bike_source)
     with Image.open(os.path.join(pokered, bike_png)) as image:
         bike_width, bike_height = image.size
-    return {
+    out_manifest = {
         "order": out,
         "bike": {
             "label": "RedBikeSprite",
@@ -289,6 +289,20 @@ def sprite_metadata(pokered, order):
             "imageHeight": bike_height,
         },
     }
+    # Yellow-only: the surfing-Pikachu overworld ride sheet, parallel
+    # to the bike entry; absent in Red/Blue. (RFC 0001)
+    surf_source = files.get("SurfingPikachuSprite")
+    if surf_source:
+        surf_png = re.sub(r"\.2bpp$", ".png", surf_source)
+        with Image.open(os.path.join(pokered, surf_png)) as image:
+            surf_width, surf_height = image.size
+        out_manifest["surfPikachu"] = {
+            "label": "SurfingPikachuSprite",
+            "imageBase": "surfing_pikachu",
+            "imageWidth": surf_width,
+            "imageHeight": surf_height,
+        }
+    return out_manifest
 
 
 def text_metadata(pokered):

tools/make_yellow_manifest.py

@@ -103,6 +103,10 @@ YELLOW_EXTRA_SYMBOLS = (
     "Pic_e5b7d", "Pic_e5ddd", "GFX_e6020", "Pic_e6340", "Pic_e6587",
     "Pic_e67d6", "GFX_e6e6f", "GFX_e718f", "GFX_e74af", "Pic_e77cf",
     "Pic_f0abf", "Pic_f0cf4",
+    # Yellow-only overworld player surf sprite, loaded outside
+    # SpriteSheetPointerTable (LoadSurfingPlayerSpriteGraphics2) --
+    # needs its own extract like RedBikeSprite. (RFC 0001)
+    "SurfingPikachuSprite",
 )
 
 # Yellow-only dialogue whose bank labels carry no leading underscore, so

tools/rom_manifest_yellow.json

@@ -19934,7 +19934,13 @@
         "imageWidth": 16,
         "label": "GamblerAsleepSprite"
       }
-    ]
+    ],
+    "surfPikachu": {
+      "imageBase": "surfing_pikachu",
+      "imageHeight": 96,
+      "imageWidth": 16,
+      "label": "SurfingPikachuSprite"
+    }
   },
   "symbols": {
     "AbraPicBack": [
@@ -21369,6 +21375,22 @@
       28,
       16822
     ],
+    "FanClubChairPrintText1": [
+      43,
+      22070
+    ],
+    "FanClubChairPrintText2": [
+      43,
+      22210
+    ],
+    "FanClubChairPrintText3": [
+      43,
+      22243
+    ],
+    "FanClubChairPrintText4": [
+      43,
+      22257
+    ],
     "FarfetchdPicBack": [
       10,
       28976
@@ -25293,6 +25315,18 @@
       24,
       22540
     ],
+    "SSAnneKitchenCook7EelsAuBarbecueText": [
+      38,
+      21363
+    ],
+    "SSAnneKitchenCook7PrimeBeefSteakText": [
+      38,
+      21414
+    ],
+    "SSAnneKitchenCook7SalmonDuSaladText": [
+      38,
+      21298
+    ],
     "SSAnneKitchenCook7Text": [
       24,
       22545
@@ -26069,10 +26103,18 @@
       21,
       25898
     ],
+    "SilphCo9FNurseDontGiveUpText": [
+      38,
+      30668
+    ],
     "SilphCo9FNurseText": [
       23,
       22467
     ],
+    "SilphCo9FNurseThankYouText": [
+      38,
+      30683
+    ],
     "SilphCo9FNurseYouLookTiredText": [
       38,
       30622
@@ -26237,10 +26279,18 @@
       32,
       25380
     ],
+    "SurfingPikachuSprite": [
+      63,
+      28143
+    ],
     "SwimmerPic": [
       19,
       20787
     ],
+    "TMNotebookText": [
+      39,
+      27310
+    ],
     "TamerPic": [
       19,
       23374
@@ -26753,6 +26803,10 @@
       6,
       21103
     ],
+    "ViridianCityFisherYouCanHaveThisText": [
+      45,
+      18396
+    ],
     "ViridianCityGambler1Text": [
       6,
       21055
@@ -26801,6 +26855,14 @@
       6,
       21043
     ],
+    "ViridianCityYoungster2CaterpieAndWeedleDescriptionText": [
+      45,
+      18125
+    ],
+    "ViridianCityYoungster2OkThenText": [
+      45,
+      18111
+    ],
     "ViridianCityYoungster2Text": [
       6,
       21067
@@ -39174,7 +39236,30 @@
       ]
     },
     "labels": [
+      "FanClubChairPrintText1",
+      "FanClubChairPrintText2",
+      "FanClubChairPrintText3",
+      "FanClubChairPrintText4",
+      "MelanieBulbasaurText",
+      "MelanieOddishText",
+      "MelanieSandshrewText",
+      "MelanieText1",
+      "MelanieText2",
+      "MelanieText3",
+      "MelanieText4",
+      "MelanieText5",
+      "SSAnneKitchenCook7EelsAuBarbecueText",
+      "SSAnneKitchenCook7PrimeBeefSteakText",
+      "SSAnneKitchenCook7SalmonDuSaladText",
       "SilphCo2FSilphWorkerFPleaseTakeThisText",
+      "SilphCo9FNurseDontGiveUpText",
+      "SilphCo9FNurseThankYouText",
+      "SilphCo9FNurseYouLookTiredText",
+      "TMNotebookText",
+      "TeachingHMsText",
+      "ViridianCityFisherYouCanHaveThisText",
+      "ViridianCityYoungster2CaterpieAndWeedleDescriptionText",
+      "ViridianCityYoungster2OkThenText",
       "_AIBattleUseItemText",
       "_AIBattleWithdrawText",
       "_AbandonLearningText",
@@ -41860,15 +41945,7 @@
       "_YeahText",
       "_YourNameIsText",
       "_ZapdosDexEntry",
-      "_ZubatDexEntry",
-      "MelanieText1",
-      "MelanieText2",
-      "MelanieText3",
-      "MelanieText4",
-      "MelanieText5",
-      "MelanieBulbasaurText",
-      "MelanieOddishText",
-      "MelanieSandshrewText"
+      "_ZubatDexEntry"
     ],
     "pointers": {
       "AgathasRoom": {