refactor: move transaction management from services to API endpoints

- Services now use db.flush() instead of db.commit() for database operations
- API endpoints handle transaction commit after service calls
- Remove db.rollback() from services (let exception handlers manage this)
- Ensures consistent transaction boundaries at API layer

This pattern gives API endpoints full control over when to commit,
allowing for better error handling and potential multi-operation transactions.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/services/content_page_service.py

@@ -211,7 +211,7 @@ class ContentPageService:
         )
 
         db.add(page)
-        db.commit()
+        db.flush()
         db.refresh(page)
 
         logger.info(
@@ -288,7 +288,7 @@ class ContentPageService:
         if updated_by is not None:
             page.updated_by = updated_by
 
-        db.commit()
+        db.flush()
         db.refresh(page)
 
         logger.info(f"Updated content page: id={page_id}, slug={page.slug}")
@@ -313,7 +313,6 @@ class ContentPageService:
             return False
 
         db.delete(page)
-        db.commit()
 
         logger.info(f"Deleted content page: id={page_id}, slug={page.slug}")
         return True