feat(app): stabilize board viewport across workspace changes

[nmrtist]

Summary

• Make the board camera layout-independent by storing its world-space center.
• Preserve fit intent across sidebar, task-card, and workspace geometry changes.
• Keep floating task cards within the central board and avoid them when fitting frames.
• Improve sidebar sizing and layer-row controls, including truncation and visibility/lock actions.
• Update persisted board-view snapshots and dependency advisories.

Testing

• cargo pr-check