Fix Gemini 3.5 Flash atlas flip and GPT-5.5 xhigh movement mirror

- gemini-3-5-flash: ATLAS_COORDS and the canvas tiles share a top-origin
  row convention, but default flipY=true mirrored sampling (row r read
  row 3-r): grass tops became purple crystal, sides hit the alpha-holed
  portal/leaves tiles (the "transparent blocks"). flipY=false, 1 line.
- gpt-5-5-xhigh: movement Z component sign-flipped against the -Z
  camera convention, mirroring all motion across the X axis (A/D
  swapped facing +-X). Negated Z, 1 line.

Run notes now carry full provenance: GPT-5.5 Pro Extended Pro, Codex
CLI (no skills) for xhigh, AntiGravity high for both Geminis, and the
local Grok Build TUI.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

outputs/gemini-3-5-flash/mythos-craft.html

@@ -1023,6 +1023,7 @@
 
             // Return texture
             const texture = new THREE.CanvasTexture(canvas);
+            texture.flipY = false; // fix: tiles are drawn with top-origin rows matching ATLAS_COORDS, but default flipY=true mirrored the rows (grass sampled the purple crystal/portal tiles, alpha holes made solid blocks see-through)
             texture.magFilter = THREE.NearestFilter;
             texture.minFilter = THREE.NearestFilter;
             return texture;