Feat(canvas): Add temporary bbox move with C key hold

[DustyShoe]

Summary

This PR adds bbox hotkey behavior for canvas. A short tap on C selects the bbox tool, and holding C temporarily activates bbox until the key is released.

This PR also moves temporary bbox hotkey handling into the shared canvas tool state so it works correctly with the existing temporary Space and Alt tool overrides. Persistent tool changes now update the base tool consistently, and focused tests were added for tap, hold, and nested temporary hotkey flows.

As a result it touches more files than it was originally expected.

Related Issues / Discussions

N/A

QA Instructions

1. Open the canvas and select a non-bbox tool such as brush.
2. Press and release C quickly. Verify that bbox becomes the selected tool.
3. Select brush or another tool again, then hold C. Verify that bbox is active only while C is held and that releasing C returns to the previous tool.
4. Hold C, then hold Space, release C, then release Space. Verify that the active tool returns to the original base tool and does not stay on bbox.
5. Repeat step 4 with Alt instead of Space and verify the active tool still returns correctly.
6. Click the bbox toolbar button and verify that it still performs a normal persistent tool switch.

Merge Plan

No special merge plan.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)