feat: implement Phase 2 stabilization

- Cache Graph API tokens with expiry-aware reuse in graph/auth.py
- Add tenacity-based retry/backoff wrapper (utils/http.py) and apply to all Graph/source API calls
- Add Pydantic request/response models (models/api.py) and FastAPI query constraints
- Add unit tests for event_model, auth and integration tests for API endpoints
- Configure ruff linter/formatter in pyproject.toml
- Add GitHub Actions CI pipeline (.github/workflows/ci.yml)
- Add requirements-dev.txt with pytest, mongomock, httpx, ruff
- Clean up typing imports and fix ruff linting across codebase

backend/routes/fetch.py

@@ -1,12 +1,12 @@
-from fastapi import APIRouter, HTTPException, Depends
-from pymongo import UpdateOne
-
-from database import events_collection
-from graph.audit_logs import fetch_audit_logs
-from sources.unified_audit import fetch_unified_audit
-from sources.intune_audit import fetch_intune_audit
-from models.event_model import normalize_event
 from auth import require_auth
+from database import events_collection
+from fastapi import APIRouter, Depends, HTTPException, Query
+from graph.audit_logs import fetch_audit_logs
+from models.api import FetchAuditLogsResponse
+from models.event_model import normalize_event
+from pymongo import UpdateOne
+from sources.intune_audit import fetch_intune_audit
+from sources.unified_audit import fetch_unified_audit
 
 router = APIRouter(dependencies=[Depends(require_auth)])
 
@@ -40,8 +40,8 @@ def run_fetch(hours: int = 168):
     return {"stored_events": len(normalized), "errors": errors}
 
 
-@router.get("/fetch-audit-logs")
-def fetch_logs(hours: int = 168):
+@router.get("/fetch-audit-logs", response_model=FetchAuditLogsResponse)
+def fetch_logs(hours: int = Query(default=168, ge=1, le=720)):
     try:
         return run_fetch(hours=hours)
     except Exception as exc: