Feat(canvas): add contextual tool hints to header bar

[DustyShoe]

Summary

This PR adds contextual canvas tool hints to the header bar for the active tool.

As the number of canvas tools and tool modifiers has grown, the need for quick in-context guidance has grown with it. Since the canvas does not currently have a bottom status bar, the top header bar was the most practical place to surface these hints without adding a new layout region.

The implementation adds a dedicated header actions component, a centralized hint mapping for canvas tools, and focused tests for the hint-selection logic. It also keeps tab labels higher priority than hints at narrow widths by clipping the hint area instead of shrinking tabs.

Related Issues / Discussions

N/A

QA Instructions

1. Open the canvas workspace and switch between tools such as brush, eraser, lasso, bbox, and text.
2. Verify the header bar shows the correct hints for the active tool.
3. Start a text session and verify Enter, Shift+Enter, and Esc hints appear.
4. Narrow the window and verify the tab strip keeps priority while the right-side hints clip at the edge instead of squeezing tabs.

Merge Plan

Simple merge.

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)