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/api/v1/vendor/team.py

@@ -150,6 +150,7 @@ def invite_team_member(
             email=invitation.email,
             role_name="staff",
         )
+    db.commit()
 
     logger.info(
         f"Invitation sent: {invitation.email} to {vendor.vendor_code} "
@@ -189,6 +190,7 @@ def accept_invitation(acceptance: InvitationAccept, db: Session = Depends(get_db
         first_name=acceptance.first_name,
         last_name=acceptance.last_name,
     )
+    db.commit()
 
     logger.info(
         f"Invitation accepted: {result['user'].email} "
@@ -272,6 +274,7 @@ def update_team_member(
         new_role_id=update_data.role_id,
         is_active=update_data.is_active,
     )
+    db.commit()
 
     logger.info(
         f"Team member updated: {user_id} in {vendor.vendor_code} "
@@ -307,6 +310,7 @@ def remove_team_member(
     vendor = request.state.vendor
 
     vendor_team_service.remove_team_member(db=db, vendor=vendor, user_id=user_id)
+    db.commit()
 
     logger.info(
         f"Team member removed: {user_id} from {vendor.vendor_code} "
@@ -344,6 +348,8 @@ def bulk_remove_team_members(
             failed_count += 1
             errors.append({"user_id": user_id, "error": str(e)})
 
+    db.commit()
+
     logger.info(
         f"Bulk remove completed: {success_count} removed, {failed_count} failed "
         f"in {vendor.vendor_code}"