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- Archive outdated design experiments and Discord-specific assets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/ws/events.ts

@@ -5,7 +5,7 @@ import { connectionManager } from './handler.js';
 import type { VoiceRoom, DmRoomMeta, ServerRoomMeta } from './handler.js';
 import { isMember, getChannelServerId, isDmMember, hasPermission, PermissionBits } from '../utils/permissions.js';
 import { broadcastDmMessage, getDmMessageWithUser } from '../routes/dm.js';
-import type { User, MessageWithUser, Attachment, DmMessageWithUser } from '@opencord/shared';
+import type { User, MessageWithUser, Attachment, DmMessageWithUser } from '@backspace/shared';
 
 function sanitizeUser(row: typeof schema.users.$inferSelect): User {
   return {

packages/server/src/ws/handler.ts

@@ -15,7 +15,7 @@ import type {
   ServerFolder,
   ReadState,
   ActiveCallInfo,
-} from '@opencord/shared';
+} from '@backspace/shared';
 
 // SQLite's SQLITE_MAX_VARIABLE_NUMBER default is 999.
 // Chunk inArray() calls to stay safely under this limit.