Feature: Undo (Ctrl+Z) support for manual canvas actions

[crewletapp]

Problem

When a user manually deletes a component on the canvas, there is no way to undo the action. The canvas currently has no undo/redo stack for manual edits — Ctrl+Z / Cmd+Z is not wired up for canvas interactions.

The only recovery path today is:

• Roll back via version history (only captures AI-driven changes, not manual edits)
• Re-describe the component in chat and ask Claude to recreate it

This is a poor UX, especially for accidental deletions.

Proposed Solution

Implement an undo/redo stack for manual canvas actions, with keyboard shortcuts:

• Ctrl+Z / Cmd+Z → Undo last action
• Ctrl+Shift+Z / Cmd+Shift+Z → Redo

Actions that should be undoable:

• Component deletion
• Component moves / repositioning
• Any other direct canvas manipulations

Notes

• The backend already has a robust version history and rollback system (DraftHistoryService) for AI-generated changes — this request is specifically for client-side undo of manual canvas edits
• The canvas keyboard handler in apps/frontend/components/workspace/canvas/index.tsx is the right place to wire up the shortcut
• A simple in-memory undo stack (e.g. using a state array of canvas snapshots) would likely be sufficient for a first pass