fix: remove unnecessary Y-flip when sampling Mode7 texture

The texture2D call was flipping the UV Y coordinate (1.0 - uv.y)
before sampling, which is no longer needed. Simplify to use UV
coordinates directly.

src/games/superkart/SuperKartMode7.js

@@ -62,7 +62,7 @@ void main () {
   if (uv.x < 0.0 || uv.x > 1.0 || uv.y < 0.0 || uv.y > 1.0) {
     col = uFog;
   } else {
-    col = texture2D(iChannel0, vec2(uv.x, 1.0 - uv.y)).rgb;
+    col = texture2D(iChannel0, uv).rgb;
   }
   float fog = smoothstep(uFogRange.x, uFogRange.y, z);
   gl_FragColor = vec4(mix(col, uFog, fog), 1.0);

src/games/superkart/sprites.md

@@ -0,0 +1,106 @@
+# Super Kart — spritesheets needed
+
+Everything below renders procedurally (tinted silhouettes, painted horizons)
+until real art is dropped in, so none of this blocks the game working — but
+here's the full list of what to paint, sized and ordered exactly as the code
+expects. Drop-in paths are wired through `data/superkart-artwork.json` (set
+`path` there once a PNG exists — no code changes needed) except for the menu
+background, which is a single fixed file.
+
+All racer/theme/item art needs a **transparent background**.
+
+## 1. Racer karts — one sheet per racer
+
+9 sheets, one per entry in `data/superkart-racers.json`:
+
+| id | display name |
+|---|---|
+| `mario` | Mario |
+| `kona` | Kona |
+| `fireball` | Fireball |
+| `smasher` | The Smasher |
+| `croc` | Croc |
+| `gerome` | Gerome |
+| `blackwind` | Blackwind |
+| `dv-8-2303` | DV-8-2303 |
+| `zanthor` | Zanthor |
+
+- **Frame size:** 64×64
+- **Layout:** 18 frames in a single row → **1152×64 px**
+- **File:** set `racerSheets.<id>.path` in `data/superkart-artwork.json`
+- **Frames 0–15** — the kart viewed from 16 angles, rotating **clockwise as
+  seen from above**, in 22.5° steps:
+  - frame 0 = dead-on from **behind**
+  - frame 4 = kart's left side
+  - frame 8 = head-on (facing the viewer)
+  - frame 12 = kart's right side
+- **Frames 16–17** — optional player-view lean frames (16 = leaning left,
+  17 = leaning right), used only for the player's fixed on-screen kart while
+  steering. If the sheet is only 16 frames wide, the game reuses frame 0 with
+  a programmatic tilt instead — fine to skip.
+- Kart centered horizontally in each frame, wheels touching the bottom edge
+  (world sprites are anchored a bit above the frame's bottom, not dead
+  center, so keep the kart's visual weight low in the frame).
+
+## 2. Theme decor — one sheet per track theme
+
+6 sheets, one per theme in `data/superkart-rules.json`:
+
+| theme id | decor order (frame 0, 1, 2 — frames 3–7 spare) |
+|---|---|
+| `beach` | palm, umbrella, rock |
+| `volcano` | boulder, vent, spire |
+| `scrapyard` | tirepile, crane, wreck |
+| `swamp` | cypress, reeds, log |
+| `speedway` | grandstand, billboard, flagpole |
+| `nightcity` | tower, neon, lamppost |
+
+- **Frame size:** 64×64
+- **Layout:** 8 frames in a single row → **512×64 px** (only the first 3 are
+  currently used per theme; the rest are free for future decor)
+- **File:** set `themeSheets.<theme>.path` in `data/superkart-artwork.json`
+- Drawn perspective-scaled beside the track, anchored near the bottom of the
+  frame like the karts above.
+
+## 3. Backdrops — one horizon strip per theme
+
+6 images, same theme ids as above.
+
+- **Size:** 1024×300 px
+- **File:** set `backdrops.<theme>.path` in `data/superkart-artwork.json`
+- Must **tile horizontally** — left and right edges need to match, since it's
+  scrolled as the camera rotates through a full 360°.
+- Drawn above the horizon line; the bottom edge's color should blend toward
+  that theme's `fog` color in `data/superkart-rules.json` so the seam into
+  the 3D ground plane is invisible.
+
+## 4. Item icons — one shared sheet
+
+- **Frame size:** 48×48
+- **Layout:** 9 frames in a single row → **432×48 px**
+- **File:** set `itemSheet.path` in `data/superkart-artwork.json`
+- **Frame order** (matches `items` in `data/superkart-rules.json`, plus two
+  extras):
+  0. bolt
+  1. seeker
+  2. oil
+  3. turbo
+  4. overdrive
+  5. emp
+  6. coins
+  7. item box (the question-mark-style box karts drive through)
+  8. single coin (the pickup, distinct from the "coins" item icon in frame 6)
+
+## 5. Main menu background — single image
+
+- **File:** `assets/images/superkart-background.png` (already exists —
+  registered directly in `src/data/assetManifest.js`, not through the
+  drop-in artwork JSON)
+- **Size:** ~1920×1080 (16:9); current art is 1928×1088 and gets stretched
+  to fill the canvas, so keep close to that aspect ratio for future updates
+  or revisions
+- Shown behind the menu, class/racer select, cup/track select, results, and
+  podium screens (anywhere that isn't an active race — the Mode 7 ground
+  fully covers it during racing). The game draws a ~45%-alpha dark scrim
+  over it for text contrast, so avoid relying on fine detail or very light
+  colors in areas where UI text sits (title/top band, center column).