Fix #10297: dispatch canvas.zoom event on double-click annotation zoom

[DanielBorgs]

Motivation and context

Fixes #10297

When zooming into an annotation via double-click, issue labels shown in review mode would incorrectly scale up with the canvas transform. This happened because the onFocusRegion method in canvasView.ts was not dispatching the canvas.zoom custom event after zooming, unlike the scroll wheel zoom handler which already dispatched it correctly.

The canvas.zoom event is used by the UI to recalculate and counteract the CSS transform applied to issue labels, keeping their font size constant regardless of zoom level. Since onFocusRegion never fired this event, the labels would scale up visually when using double-click zoom.

The fix dispatches canvas.zoom at the end of onFocusRegion, matching the existing behavior of the scroll wheel zoom handler.

How has this been tested?

Manual testing:

Created a task, opened a job in review mode, created an issue on an annotation, and verified that double-click zooming no longer scales up the issue label text.

Automated testing:

Added a Cypress e2e test in tests/cypress/e2e/issues_prs2/issue_10297_zooming_in_onto_annotation_increases_issue_text_size.js that patches EventTarget.prototype.dispatchEvent and asserts that a canvas.zoom event is fired when double-clicking an annotation shape.

Checklist

• I submit my changes into the develop branch
• I have created a changelog fragment
  [ ] I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (see GitHub docs)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.

[DanielBorgs]

Hi @bsekachev, @nmanovic, just pinging on this for a review when you have a chance! Let me know if you need any adjustments.

Also, the rest_api_testing job failed due to a transient Docker Hub TLS timeout when pulling the cvat_opa image, unrelated to these changes. I believe a rerun should be enough to clear it.