fix(client): eliminate unreachable code in Close method

Refactor Close() to use early return pattern, removing unreachable
return statement that occurred when c.db was nil. The new implementation
checks for nil database first, making the control flow clearer and
eliminating the code path that could never be executed.

Author: sgaunet

internal/app/client.go

@@ -40,12 +40,12 @@ func (c *PostgreSQLClientImpl) Connect(connectionString string) error {
 
 // Close closes the database connection.
 func (c *PostgreSQLClientImpl) Close() error {
-	if c.db != nil {
-		if err := c.db.Close(); err != nil {
-			return fmt.Errorf("failed to close database: %w", err)
-		}
+	if c.db == nil {
 		return nil
 	}
+	if err := c.db.Close(); err != nil {
+		return fmt.Errorf("failed to close database: %w", err)
+	}
 	return nil
 }