chore: code quality audit and lint fixes

- Fix all 63 ESLint errors across codebase
- Consolidate MaterialWithTextureSlots type in src/types/three/three.ts
- Add CSS custom properties for design tokens
- Extract ebike constants to src/data/ebike/ebikeConfig.ts
- Add proper TypeScript types for window extensions
- Fix React hooks violations (refs during render, setState in effects)
- Remove unused exports and redundant CSS
- Add type guards for Three.js material handling
- Clean up AI slop comments and legacy CSS patterns

src/data/galleryModels.ts

@@ -4,10 +4,6 @@ export interface GalleryModel {
   path: string;
 }
 
-/**
- * List of 3D models available in the gallery.
- * Only includes models that exist in `/public/models/`.
- */
 export const galleryModels: GalleryModel[] = [
   { id: "arbre", name: "Arbre", path: "/models/arbre/model.gltf" },
   { id: "blocking", name: "Blocking", path: "/models/blocking/terrain.gltf" },