Integrate account sync with API, background tasks, and user creation

Integration Components:
1. Manual API Endpoints (admin-only):
   - POST /api/v1/admin/accounts/sync (full sync)
   - POST /api/v1/admin/accounts/sync/{account_name} (single account)

2. Scheduled Background Sync:
   - Hourly background task (wait_for_account_sync)
   - Registered in castle_start() lifecycle
   - Automatically syncs new accounts from Beancount to Castle DB

3. Auto-sync on User Account Creation:
   - Updated get_or_create_user_account() in crud.py
   - Uses sync_single_account_from_beancount() for consistency
   - Ensures receivable/payable accounts are synced when users register

Flow:
- User associates wallet → creates receivable/payable in Beancount
  → syncs to Castle DB → permissions can be granted
- Admin manually syncs → all Beancount accounts added to Castle DB
- Hourly task → catches any accounts created directly in Beancount

This ensures Beancount remains the source of truth while Castle DB
maintains metadata for permissions and user associations.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tasks.py

@@ -95,6 +95,59 @@ async def scheduled_daily_reconciliation():
         raise
 
 
+async def scheduled_account_sync():
+    """
+    Scheduled task that runs hourly to sync accounts from Beancount to Castle DB.
+
+    This ensures Castle DB stays in sync with Beancount (source of truth) by
+    automatically adding any new accounts created in Beancount to Castle's
+    metadata database for permission tracking.
+    """
+    from .account_sync import sync_accounts_from_beancount
+
+    logger.info(f"[CASTLE] Running scheduled account sync at {datetime.now()}")
+
+    try:
+        stats = await sync_accounts_from_beancount(force_full_sync=False)
+
+        if stats["accounts_added"] > 0:
+            logger.info(
+                f"[CASTLE] Account sync: Added {stats['accounts_added']} new accounts"
+            )
+
+        if stats["errors"]:
+            logger.warning(
+                f"[CASTLE] Account sync: {len(stats['errors'])} errors encountered"
+            )
+            for error in stats["errors"][:5]:  # Log first 5 errors
+                logger.error(f"  - {error}")
+
+        return stats
+
+    except Exception as e:
+        logger.error(f"[CASTLE] Error in scheduled account sync: {e}")
+        raise
+
+
+async def wait_for_account_sync():
+    """
+    Background task that periodically syncs accounts from Beancount to Castle DB.
+
+    Runs hourly to ensure Castle DB stays in sync with Beancount.
+    """
+    logger.info("[CASTLE] Account sync background task started")
+
+    while True:
+        try:
+            # Run sync
+            await scheduled_account_sync()
+        except Exception as e:
+            logger.error(f"[CASTLE] Account sync error: {e}")
+
+        # Wait 1 hour before next sync
+        await asyncio.sleep(3600)  # 3600 seconds = 1 hour
+
+
 def start_daily_reconciliation_task():
     """
     Initialize the daily reconciliation task.