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- Archive outdated design experiments and Discord-specific assets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

@@ -93,7 +93,7 @@ async function main(): Promise<void> {
 
   try {
     await app.listen({ port: config.port, host: config.host });
-    console.log(`Opencord server running at http://${config.host}:${config.port}`);
+    console.log(`Backspace server running at http://${config.host}:${config.port}`);
   } catch (err) {
     app.log.error(err);
     process.exit(1);