feat: wire chat to the agent loop (POST /chat)

- api: /chat route runs runAgent (session-required, 503 when unconfigured)
- api: index.ts builds OpenRouterLlmClient + WpRestExecutor from env; loads .env
- web: useChat calls /chat with mock fallback; proxy /chat+/sites+/health
- .env.example: DATABASE_URL empty by default (in-memory dev)
- 111 unit tests green; smoke-tested signup+chat

web/vite.config.ts

@@ -6,6 +6,9 @@ export default defineConfig({
   server: {
     proxy: {
       '/auth': 'http://localhost:3000',
+      '/chat': 'http://localhost:3000',
+      '/sites': 'http://localhost:3000',
+      '/health': 'http://localhost:3000',
     },
   },
   test: {