fix: health_check timeout 3→5초 — MLX cold start 대응

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nanoclaude/services/model_adapter.py

@@ -100,9 +100,9 @@ class ModelAdapter:
             return data["choices"][0]["message"]["content"]
 
     async def health_check(self) -> bool:
-        """GET /v1/models — 3초 timeout."""
+        """GET /v1/models — 5초 timeout."""
         try:
-            async with httpx.AsyncClient(timeout=3.0) as client:
+            async with httpx.AsyncClient(timeout=5.0) as client:
                 resp = await client.get(f"{self.base_url}/v1/models")
                 return resp.status_code < 500
         except Exception: