feat: Phase 1+2 — project setup and core infrastructure

- requirements.txt, config.yaml, .env, Dockerfile, docker-compose.yml
- app/core: config (YAML+env override), logging (JSON structured),
  exceptions (typed hierarchy), json_utils (Markdown fence stripping)
- app/clients: LLMClient ABC + ZhipuAIClient (run_in_executor),
  StorageClient ABC + RustFSClient (boto3 head_object for size check)
- app/main.py: FastAPI app with health endpoint and router registration
- app/core/dependencies.py: lru_cache singleton factories
- tests/conftest.py: mock_llm, mock_storage, test_app, client fixtures
- pytest.ini: asyncio_mode=auto
- 11 unit tests passing

app/clients/storage/base.py

@@ -0,0 +1,21 @@
+from abc import ABC, abstractmethod
+
+
+class StorageClient(ABC):
+    @abstractmethod
+    async def download_bytes(self, bucket: str, path: str) -> bytes:
+        """Download an object and return its raw bytes."""
+
+    @abstractmethod
+    async def upload_bytes(
+        self, bucket: str, path: str, data: bytes, content_type: str = "application/octet-stream"
+    ) -> None:
+        """Upload raw bytes to the given bucket/path."""
+
+    @abstractmethod
+    async def get_presigned_url(self, bucket: str, path: str, expires: int = 3600) -> str:
+        """Return a presigned GET URL valid for `expires` seconds."""
+
+    @abstractmethod
+    async def get_object_size(self, bucket: str, path: str) -> int:
+        """Return the object size in bytes without downloading it."""