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- Archive outdated design experiments and Discord-specific assets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

@@ -47,7 +47,7 @@ export const config = {
   },
 
   uploadDir: env('UPLOAD_DIR', resolve(__dirname, '../../../data/uploads')),
-  dbPath: env('DB_PATH', resolve(__dirname, '../../../data/opencord.db')),
+  dbPath: env('DB_PATH', resolve(__dirname, '../../../data/backspace.db')),
   maxUploadSize: envInt('MAX_UPLOAD_SIZE', 104857600),
   registrationOpen: envBool('REGISTRATION_OPEN', true),
 } as const;