feat(ui): make project switching undoable with Ctrl+Z (PUNT-411)

[jmynes]

Summary

• Adds a projectSwitch undo action type to the undo store, tracking the source/target project IDs, names, and paths
• When clicking a different project in the sidebar, an undo entry is pushed so Ctrl+Z navigates back to the previous project
• Ctrl+Y / Ctrl+Shift+Z re-applies the project switch (redo)
• Toast notifications confirm each switch ("Switched back" / "Switched to project")

Test plan

• Navigate between two projects via the sidebar
• Press Ctrl+Z — should navigate back to the previous project with a "Switched back" toast
• Press Ctrl+Y — should navigate forward again with a "Switched to project" toast
• Verify clicking the same project (already active) does NOT push an undo entry
• Verify switching projects when no project was previously active does NOT push an undo entry
• Verify other undo/redo actions (delete, move, etc.) still work correctly

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