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>

wrangler.toml

@@ -1,8 +1,10 @@
-name = "opennext-app"
-main = ".open-next/worker.js"
-compatibility_date = "2024-09-23"
+name = "edge-proxy-relay"
+main = "src/index.ts"
+compatibility_date = "2024-12-01"
 compatibility_flags = ["nodejs_compat"]
 
-[assets]
-directory = ".open-next/assets"
-binding = "ASSETS"
+[vars]
+NODE_VERSION = "22"
+
+[env.production]
+name = "edge-proxy-relay-prod"