Wraps PDOStatement::fetchObject as pdo/fetch-object: (fetch-object stmt & [class-name ctor-args]). Returns the next row as an object - stdClass by default, or an instance of class-name (with optional constructor args) - and nil when the result set is exhausted.

Return-shape decision (per #11)

Converting to a map would make this identical to fetch, adding nothing. The wrapper's value is hydrating rows into a named class, so it returns the PHP object as PDO produces it. The default stdClass path is kept for callers who prefer object access. false (no row) is normalised to nil, matching fetch.

• Removed from the "Not implemented yet" block in src/pdo/statement.phel.
• Tests: fetch-object-returns-stdclass-row (class + property) and fetch-object-returns-nil-when-no-rows.
• README API table + CHANGELOG ## [Unreleased] updated.

Polish pass: no refactor needed - when-let mirrors the nil-guard idiom already used by fetch.

composer test green (38 assertions).

Closes #11