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- Archive outdated design experiments and Discord-specific assets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

@@ -2,7 +2,7 @@ import type { FastifyInstance } from 'fastify';
 import { eq } from 'drizzle-orm';
 import { getDb, schema } from '../db/index.js';
 import { authenticate } from '../utils/auth.js';
-import type { InstanceStreamingLimits } from '@opencord/shared';
+import type { InstanceStreamingLimits } from '@backspace/shared';
 
 const VALID_RESOLUTIONS = [540, 720, 1080];
 const VALID_FRAMERATES = [30, 45, 60];