Add integration test for imagify_after_optimize hook

[Miraeld]

🤖 AI-generated — created by an automated pipeline. Review before acting on this.

Source: Follow-up from QA on #1126 (COULD_HAVE)

Context
The new classes/Tracking/Subscriber registers on imagify_after_optimize, but there is no integration test verifying the full hook-to-event-fire chain end-to-end. Currently only unit tests with mocked dependencies cover the tracking logic.

Suggestion
Add an integration test that verifies the imagify_after_optimize hook is actually registered and wired to the Subscriber, with the full stack exercised (not just mocked dependencies).

Acceptance Criteria

• Integration test exists that fires imagify_after_optimize and verifies the Subscriber is invoked
• Test covers the full hook-to-event chain without mocking the Subscriber
• Test passes in CI

Development steps

• Create integration test file in appropriate test directory
• Set up test fixture with real Subscriber instance
• Fire imagify_after_optimize hook with test data
• Assert Subscriber callback was executed

Effort estimation
S / M