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/types/ebike/ebikeWindow.ts

@@ -0,0 +1,11 @@
+import type * as THREE from "three";
+import type { Vector3Tuple } from "@/types/three/three";
+
+declare global {
+  interface Window {
+    ebikeVisualGroup: React.RefObject<THREE.Group | null> | null;
+    ebikeParkedPosition: Vector3Tuple | null;
+    ebikeParkedRotation: number | null;
+    ebikeSteerFactor: number | undefined;
+  }
+}

src/types/three/three.ts

@@ -1,4 +1,5 @@
 import type { Octree } from "three-stdlib";
+import type * as THREE from "three";
 
 export type Vector3Tuple = [number, number, number];
 
@@ -13,3 +14,21 @@ export interface ModelTransformProps {
 export type ColliderShape = "cuboid" | "ball" | "hull";
 
 export type OctreeReadyHandler = (octree: Octree) => void;
+
+/**
+ * Keys for texture slots that may exist on various material types.
+ */
+export type TextureMaterialKey = Extract<
+  | keyof THREE.MeshBasicMaterial
+  | keyof THREE.MeshStandardMaterial
+  | keyof THREE.MeshPhysicalMaterial
+  | keyof THREE.MeshToonMaterial,
+  string
+>;
+
+/**
+ * Interface for materials that may have texture slots.
+ * Used for type-safe texture diagnostic access and disposal.
+ */
+export type MaterialWithTextureSlots = THREE.Material &
+  Partial<Record<TextureMaterialKey, THREE.Texture | null>>;