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/ebike/ebikeConfig.ts

@@ -0,0 +1,16 @@
+import type { Vector3Tuple } from "@/types/three/three";
+
+export interface CameraTransform {
+  position: Vector3Tuple;
+  rotation: Vector3Tuple;
+}
+
+export const EBIKE_CAMERA_TRANSFORM: CameraTransform = {
+  position: [-3.5, 6, 0],
+  rotation: [-10, -90, 0],
+};
+
+export const EBIKE_DROP_PLAYER_TRANSFORM: CameraTransform = {
+  position: [0, 1.5, -3],
+  rotation: [0, 0, 0],
+};