fix(qa): 5 bug fixes — audit dates, CSP, template modal, MITRE sync timeout, data source auto-sync

- audit_service: set timestamp=datetime.now(utc) explicitly so DB never stores NULL
- AuditLogPage: formatDate handles null/undefined timestamps (was showing Jan 1 1970)
- nginx.conf: add CSP script-src hash for inline script (sha256-31OgE8E9...)
- system.py: MITRE sync now runs in BackgroundTasks — returns immediately, no more 120s timeout
- mitre_sync_job.py: add _run_data_sources_sync job (every 6h) that checks sync_frequency
  and auto-syncs overdue enabled data sources
- SystemPage: MITRE sync result shows "started" vs "complete" message
- test-templates.ts: add updateTemplate() API function
- SystemPage: template name cell is now clickable — opens TemplateDetailModal with
  full edit form (name, description, procedure, detection, platform, severity, tool)
  and Save / Activate / Deactivate / Close buttons

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/routers/system.py

@@ -7,10 +7,10 @@ scheduler health introspection.
 
 import logging
 
-from fastapi import APIRouter, Depends, Request
+from fastapi import APIRouter, BackgroundTasks, Depends, Request
 from sqlalchemy.orm import Session
 
-from app.database import get_db
+from app.database import SessionLocal, get_db
 from app.dependencies.auth import require_role
 from app.models.user import User
 from app.services.mitre_sync_service import sync_mitre
@@ -24,25 +24,39 @@ logger = logging.getLogger(__name__)
 router = APIRouter(prefix="/system", tags=["system"])
 
 
+def _bg_mitre_sync() -> None:
+    """Run MITRE sync in a background task with its own DB session."""
+    logger.info("Background MITRE sync task starting...")
+    db = SessionLocal()
+    try:
+        summary = sync_mitre(db)
+        logger.info("Background MITRE sync task finished — %s", summary)
+    except Exception:
+        logger.exception("Background MITRE sync task failed")
+    finally:
+        db.close()
+
+
 @router.post("/sync-mitre")
 @limiter.limit("2/hour")
 def trigger_mitre_sync(
     request: Request,
-    db: Session = Depends(get_db),
+    background_tasks: BackgroundTasks,
     current_user: User = Depends(require_role("admin")),
 ):
-    """Manually trigger a MITRE ATT&CK synchronisation.
+    """Manually trigger a MITRE ATT&CK synchronisation in the background.
 
     **Requires** the ``admin`` role.
 
-    Returns a JSON object with the sync summary including the count of
-    new and updated techniques.
+    Returns immediately — the sync runs asynchronously. Poll
+    ``/system/scheduler-status`` for progress, or check server logs.
     """
-    summary = sync_mitre(db)
+    background_tasks.add_task(_bg_mitre_sync)
     return {
-        "message": "MITRE sync completed",
-        "new": summary["created"],
-        "updated": summary["updated"],
+        "message": "MITRE sync started in background",
+        "status": "started",
+        "new": 0,
+        "updated": 0,
     }