refactor: FastAPI best practices — return types, Pydantic schemas, middleware, code dedup

- Все 18 роутов получили return type annotations
- Создан schemas.py с Pydantic-моделями (ScanOut, PackageOut, FindingOut, ...)
- API-роуты: response_model на list/detail/export/stats
- 404 через HTTPException(404) вместо {'detail':'Not found'} (200)
- RequestLoggingMiddleware: method, path, status, duration_ms
- Глобальный exception handler: ловит необработанные исключения → 500
- _parse_flagged(): вынесен дублирующийся string→bool
- parse_package_path(): общий для web.py и api_packages.py
- selectinload: вынесены в top-level imports
- harvester: makedirs/mkdtemp/rmtree обёрнуты в asyncio.to_thread()

guarddog_nexus/main.py

@@ -1,10 +1,12 @@
 """GuardDog Nexus — FastAPI application entry point."""
 
 import os
+import time
 from contextlib import asynccontextmanager
 
 import uvicorn
 from fastapi import FastAPI, Request
+from fastapi.responses import JSONResponse
 from fastapi.staticfiles import StaticFiles
 from starlette.middleware.base import BaseHTTPMiddleware
 
@@ -56,6 +58,21 @@ async def lifespan(app: FastAPI):
     log.info("%s shutting down", APP_NAME)
 
 
+class RequestLoggingMiddleware(BaseHTTPMiddleware):
+    async def dispatch(self, request: Request, call_next):
+        start = time.monotonic()
+        response = await call_next(request)
+        duration = (time.monotonic() - start) * 1000
+        log.info(
+            "%s %s %s %.1fms",
+            request.method,
+            request.url.path,
+            response.status_code,
+            duration,
+        )
+        return response
+
+
 app = FastAPI(
     title=APP_NAME,
     version=APP_VERSION,
@@ -63,6 +80,14 @@ app = FastAPI(
     lifespan=lifespan,
 )
 app.add_middleware(LangMiddleware)
+app.add_middleware(RequestLoggingMiddleware)
+
+
+@app.exception_handler(Exception)
+async def global_exception_handler(request: Request, exc: Exception):
+    log.exception("Unhandled exception on %s %s", request.method, request.url.path)
+    return JSONResponse(status_code=500, content={"detail": "Internal server error"})
+
 
 app.include_router(webhook_router)
 app.include_router(metrics_router)
@@ -76,7 +101,7 @@ if os.path.isdir(STATIC_DIR):
 
 
 @app.get("/health")
-async def health():
+async def health() -> dict:
     return {"status": "ok", "version": APP_VERSION}