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- Archive outdated design experiments and Discord-specific assets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/hooks/useWebSocket.ts

@@ -5,7 +5,7 @@ import { useChatStore } from '../stores/chatStore';
 import { useVoiceStore } from '../stores/voiceStore';
 import { useSocialStore } from '../stores/socialStore';
 import { useSettingsStore } from '../stores/settingsStore';
-import type { ServerEvent, ClientEvent, ActiveCallInfo } from '@opencord/shared';
+import type { ServerEvent, ClientEvent, ActiveCallInfo } from '@backspace/shared';
 
 let globalWs: WebSocket | null = null;
 let reconnectAttempts = 0;