Ensure Snapshots

Ensure weekly snapshots are up to date.

Called by get_priorities MCP handler on every dashboard load. Creates missing snapshots for up to 3 completed weeks. Updates running aggregates (streak_count, total_hours_invested, avg_target_achievement).

This endpoint:

• Is idempotent (safe to call repeatedly)
• Never fails with error status (returns 200 with partial results)
• Runs in parallel with other dashboard data fetches

Args: request: FastAPI request (for http_client and correlation_id) user_id: User ID from validated JWT (via X-User-ID header) session: Database session

Returns: 200: { "success": true, "data": { "checked": 3, # Weeks checked "created": 1, # Weeks with new snapshots "errors": 0 # Weeks that failed } }