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/core/logging.py

@@ -0,0 +1,62 @@
+import json
+import logging
+import time
+from typing import Callable
+
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.requests import Request
+from starlette.responses import Response
+
+
+def get_logger(name: str) -> logging.Logger:
+    logger = logging.getLogger(name)
+    if not logger.handlers:
+        handler = logging.StreamHandler()
+        handler.setFormatter(_JsonFormatter())
+        logger.addHandler(handler)
+        logger.propagate = False
+    return logger
+
+
+class _JsonFormatter(logging.Formatter):
+    def format(self, record: logging.LogRecord) -> str:
+        payload = {
+            "time": self.formatTime(record, datefmt="%Y-%m-%dT%H:%M:%S"),
+            "level": record.levelname,
+            "logger": record.name,
+            "message": record.getMessage(),
+        }
+        if record.exc_info:
+            payload["exc_info"] = self.formatException(record.exc_info)
+        # Merge any extra fields passed via `extra=`
+        for key, value in record.__dict__.items():
+            if key not in (
+                "name", "msg", "args", "levelname", "levelno", "pathname",
+                "filename", "module", "exc_info", "exc_text", "stack_info",
+                "lineno", "funcName", "created", "msecs", "relativeCreated",
+                "thread", "threadName", "processName", "process", "message",
+                "taskName",
+            ):
+                payload[key] = value
+        return json.dumps(payload, ensure_ascii=False)
+
+
+class RequestLoggingMiddleware(BaseHTTPMiddleware):
+    def __init__(self, app, logger: logging.Logger | None = None) -> None:
+        super().__init__(app)
+        self._logger = logger or get_logger("request")
+
+    async def dispatch(self, request: Request, call_next: Callable) -> Response:
+        start = time.perf_counter()
+        response = await call_next(request)
+        duration_ms = round((time.perf_counter() - start) * 1000, 1)
+        self._logger.info(
+            "request",
+            extra={
+                "method": request.method,
+                "path": request.url.path,
+                "status": response.status_code,
+                "duration_ms": duration_ms,
+            },
+        )
+        return response