Add calendar sync utilities and Beteiligte sync cron job

- Implemented calendar_sync_utils.py for shared utility functions
  including DB connection, Google Calendar service initialization,
  Redis client setup, and employee sync operations.

- Created beteiligte_sync_cron_step.py to handle periodic sync
  of Beteiligte entities, checking for new, modified, failed,
  and stale records, and emitting sync events accordingly.

steps/advoware_cal_sync/calendar_sync_cron_step.py

@@ -0,0 +1,50 @@
+"""
+Calendar Sync Cron Step
+
+Cron trigger for automatic calendar synchronization. 
+Emits calendar_sync_all event to start sync cascade.
+"""
+import sys
+from pathlib import Path
+sys.path.insert(0, str(Path(__file__).parent))
+from calendar_sync_utils import log_operation
+
+from motia import cron, FlowContext
+
+
+config = {
+    'name': 'Calendar Sync Cron Job',
+    'description': 'Runs calendar sync automatically every 15 minutes',
+    'flows': ['advoware'],
+    'triggers': [
+        cron("0 */15 * * * *")  # Every 15 minutes (6-field: sec min hour day month weekday)
+    ],
+    'enqueues': ['calendar_sync_all']
+}
+
+
+async def handler(input_data: dict, ctx: FlowContext):
+    """Cron handler that triggers the calendar sync cascade."""
+    try:
+        log_operation('info', "Calendar Sync Cron: Starting to emit sync-all event", context=ctx)
+
+        # Enqueue sync-all event
+        await ctx.enqueue({
+            "topic": "calendar_sync_all",
+            "data": {
+                "triggered_by": "cron"
+            }
+        })
+
+        log_operation('info', "Calendar Sync Cron: Emitted sync-all event", context=ctx)
+        return {
+            'status': 'completed',
+            'triggered_by': 'cron'
+        }
+
+    except Exception as e:
+        log_operation('error', f"Fehler beim Cron-Job: {e}", context=ctx)
+        return {
+            'status': 'error',
+            'error': str(e)
+        }