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- Archive outdated design experiments and Discord-specific assets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/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "@opencord/server",
+  "name": "@backspace/server",
   "version": "1.0.0",
   "private": true,
   "type": "module",
@@ -15,7 +15,7 @@
     "@fastify/rate-limit": "^9.1.0",
     "@fastify/static": "^7.0.4",
     "@fastify/websocket": "^10.0.1",
-    "@opencord/shared": "workspace:*",
+    "@backspace/shared": "workspace:*",
     "bcryptjs": "^2.4.3",
     "better-sqlite3": "^11.3.0",
     "cheerio": "^1.0.0",