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/vendor_domain_service.py

@@ -113,7 +113,7 @@ class VendorDomainService:
             )
 
             db.add(new_domain)
-            db.commit()
+            db.flush()
             db.refresh(new_domain)
 
             logger.info(f"Domain {normalized_domain} added to vendor {vendor_id}")
@@ -126,10 +126,8 @@ class VendorDomainService:
             InvalidDomainFormatException,
             ReservedDomainException,
         ):
-            db.rollback()
             raise
         except Exception as e:
-            db.rollback()
             logger.error(f"Error adding domain: {str(e)}")
             raise ValidationException("Failed to add domain")
 
@@ -223,17 +221,15 @@ class VendorDomainService:
             if domain_update.is_active is not None:
                 domain.is_active = domain_update.is_active
 
-            db.commit()
+            db.flush()
             db.refresh(domain)
 
             logger.info(f"Domain {domain.domain} updated")
             return domain
 
         except (VendorDomainNotFoundException, DomainNotVerifiedException):
-            db.rollback()
             raise
         except Exception as e:
-            db.rollback()
             logger.error(f"Error updating domain: {str(e)}")
             raise ValidationException("Failed to update domain")
 
@@ -257,16 +253,13 @@ class VendorDomainService:
             vendor_id = domain.vendor_id
 
             db.delete(domain)
-            db.commit()
 
             logger.info(f"Domain {domain_name} deleted from vendor {vendor_id}")
             return f"Domain {domain_name} deleted successfully"
 
         except VendorDomainNotFoundException:
-            db.rollback()
             raise
         except Exception as e:
-            db.rollback()
             logger.error(f"Error deleting domain: {str(e)}")
             raise ValidationException("Failed to delete domain")
 
@@ -312,7 +305,7 @@ class VendorDomainService:
                         # Verification successful
                         domain.is_verified = True
                         domain.verified_at = datetime.now(UTC)
-                        db.commit()
+                        db.flush()
                         db.refresh(domain)
 
                         logger.info(f"Domain {domain.domain} verified successfully")