feat: JWT auth, user management, audit logging system

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/middleware/audit.py

@@ -0,0 +1,63 @@
+"""Audit middleware: log all mutating requests to AuditLog."""
+import json
+
+from fastapi import Request
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.responses import Response
+
+from app.database import async_session
+from app.models.audit import AuditLog
+from app.services.auth_service import decode_access_token, get_user_by_id
+
+
+class AuditMiddleware(BaseHTTPMiddleware):
+    async def dispatch(self, request: Request, call_next) -> Response:
+        if request.method in ("POST", "PUT", "PATCH", "DELETE"):
+            response = await call_next(request)
+            await self._log(request, response)
+            return response
+        return await call_next(request)
+
+    async def _log(self, request: Request, response: Response):
+        try:
+            user_id = "anonymous"
+            username = "anonymous"
+
+            auth_header = request.headers.get("authorization")
+            if auth_header and auth_header.startswith("Bearer "):
+                try:
+                    payload = decode_access_token(auth_header[7:])
+                    async with async_session() as db:
+                        user = await get_user_by_id(db, payload["sub"])
+                        if user:
+                            user_id = user.id
+                            username = user.username
+                except Exception:
+                    pass
+
+            path = request.url.path
+            action = f"{request.method} {path}"
+
+            detail = {}
+            if response.status_code >= 400:
+                body = b""
+                try:
+                    body = await request.body()
+                    if body:
+                        detail["request_body"] = json.loads(body)
+                except Exception:
+                    pass
+
+            async with async_session() as db:
+                log = AuditLog(
+                    user_id=user_id,
+                    username=username,
+                    action=action,
+                    target=path,
+                    detail=json.dumps(detail) if detail else None,
+                    ip_address=request.client.host if request.client else None,
+                )
+                db.add(log)
+                await db.commit()
+        except Exception:
+            pass