Add document approval workflow pause/resume integration test

[benrowe]

Summary

• Adds an integration test demonstrating a document approval workflow: a permission gate, a format-validation action, an approval-request action that pauses with metadata, then resume into a publish action and a notification action.
• Final assertion confirms the document's state transitions to published via real State::with() mutation, and that resuming doesn't re-execute already-completed actions.
• Test-only change — no src/ modifications, since pause/resume is already fully implemented.

Closes #17

Test plan

• composer test:single tests/Integration/StateFlow/DocumentApprovalWorkflowTest.php — passes (1 test, 12 assertions)
• composer lint — clean
• composer quality (PHPStan + PHPMD) — no errors
• composer test (full suite) — 405 tests, 1333 assertions, all green

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