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/code_quality_service.py

@@ -117,7 +117,7 @@ class CodeQualityService:
             )
             db.add(violation)
 
-        db.commit()
+        db.flush()
         db.refresh(scan)
 
         logger.info(f"Scan completed: {scan.total_violations} violations found")
@@ -268,7 +268,7 @@ class CodeQualityService:
             priority=priority,
         )
         db.add(assignment)
-        db.commit()
+        db.flush()
 
         logger.info(f"Violation {violation_id} assigned to user {user_id}")
         return assignment
@@ -297,7 +297,7 @@ class CodeQualityService:
         violation.resolved_by = resolved_by
         violation.resolution_note = resolution_note
 
-        db.commit()
+        db.flush()
         logger.info(f"Violation {violation_id} resolved by user {resolved_by}")
         return violation
 
@@ -325,7 +325,7 @@ class CodeQualityService:
         violation.resolved_by = ignored_by
         violation.resolution_note = f"Ignored: {reason}"
 
-        db.commit()
+        db.flush()
         logger.info(f"Violation {violation_id} ignored by user {ignored_by}")
         return violation
 
@@ -348,7 +348,7 @@ class CodeQualityService:
             violation_id=violation_id, user_id=user_id, comment=comment
         )
         db.add(comment_obj)
-        db.commit()
+        db.flush()
 
         logger.info(f"Comment added to violation {violation_id} by user {user_id}")
         return comment_obj