feat: migrate from Next.js to pure Bun relay proxy

- Replace Next.js app router with standalone Bun.serve() entry point
- Add middleware stack: rate limiter, body limiter, structured logger, SSRF protection
- Add WebSocket bidirectional relay via x-relay-target header
- Implement error classification (DNS→502, timeouts→504, SSRF→403, rate→429)
- Remove all Next.js dependencies and config files
- Update deploy workflow, tsconfig, wrangler config for Bun deployment

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -13,6 +13,7 @@ coverage
 # logs
 logs
 _.log
+*.log
 report.[0-9]_.[0-9]_.[0-9]_.[0-9]_.json
 
 # dotenv environment variable files
@@ -39,3 +40,7 @@ next-env.d.ts
 # OpenNext & Wrangler build output
 .open-next/
 .wrangler/
+
+.claude/
+
+.codegraph/