Fix FOREIGN KEY constraint failed when operating on non-existent issues

Fixes #325

- Fix CloseIssue to check rows affected before inserting event
- Fix RemoveLabel to check rows affected before inserting event
- Fix UpdateIssueID to check rows affected before inserting event
- Prevent orphan events and confusing error messages

Amp-Thread-ID: https://ampcode.com/threads/T-aa765a68-5cc4-465b-a2f6-aa008933c11e
Co-authored-by: Amp <amp@ampcode.com>

internal/storage/sqlite/labels.go

@@ -20,11 +20,20 @@ func (s *SQLiteStorage) executeLabelOperation(
 	operationError string,
 ) error {
 	return s.withTx(ctx, func(tx *sql.Tx) error {
-		_, err := tx.ExecContext(ctx, labelSQL, labelSQLArgs...)
+		result, err := tx.ExecContext(ctx, labelSQL, labelSQLArgs...)
 		if err != nil {
 			return fmt.Errorf("%s: %w", operationError, err)
 		}
 
+		rows, err := result.RowsAffected()
+		if err != nil {
+			return fmt.Errorf("failed to check rows affected: %w", err)
+		}
+		if rows == 0 {
+			// No change made (label already existed or didn't exist), so don't record event
+			return nil
+		}
+
 		_, err = tx.ExecContext(ctx, `
 			INSERT INTO events (issue_id, event_type, actor, comment)
 			VALUES (?, ?, ?, ?)