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>

tsconfig.json

@@ -1,7 +1,7 @@
 {
   "compilerOptions": {
-    "target": "ES2017",
-    "lib": ["dom", "dom.iterable", "esnext"],
+    "target": "ESNext",
+    "lib": ["esnext"],
     "allowJs": true,
     "skipLibCheck": true,
     "strict": true,
@@ -11,24 +11,15 @@
     "moduleResolution": "bundler",
     "resolveJsonModule": true,
     "isolatedModules": true,
-    "jsx": "react-jsx",
     "types": ["bun-types"],
     "incremental": true,
-    "plugins": [
-      {
-        "name": "next"
-      }
-    ],
     "paths": {
       "@/*": ["./src/*"]
     }
   },
   "include": [
-    "next-env.d.ts",
     "**/*.ts",
     "**/*.tsx",
-    ".next/types/**/*.ts",
-    ".next/dev/types/**/*.ts",
     "**/*.mts"
   ],
   "exclude": ["node_modules"]