feat: add Backspace design prototype and rebrand from Opencord

- Add Backspace-design-prototype.html: finalized "Aether Drift" design
  language with warm matte surfaces and subtle frosted glass accents
- Update CLAUDE.md with DESIGN SYSTEM section and remove Discord clone references
- Rename all Opencord references to Backspace across the full codebase
- Archive outdated design experiments and Discord-specific assets
- Add science-backed accessibility fallback (prefers-reduced-transparency)

packages/web/src/api/client.ts

@@ -26,12 +26,12 @@ import type {
   Friend,
   FriendRequest,
   InstanceStreamingLimits,
-} from '@opencord/shared';
+} from '@backspace/shared';
 
 const BASE_URL = '/api';
 
 function getToken(): string | null {
-  return localStorage.getItem('opencord_token');
+  return localStorage.getItem('backspace_token');
 }
 
 async function request<T>(