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- Archive outdated design experiments and Discord-specific assets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/server/src/utils/permissions.ts

@@ -5,7 +5,7 @@ import {
   ALL_PERMISSIONS,
   stringToPermissions,
   permissionsToString,
-} from '@opencord/shared/src/permissions.js';
+} from '@backspace/shared/src/permissions.js';
 
 // Re-export for convenience
 export { PermissionBits, ALL_PERMISSIONS, permissionsToString, stringToPermissions };