Undo/redo for dashboards

**What the feature is (as Title)**
Undo/redo for dashboards

**Value proposition**
Standard Cmd/Ctrl+Z and Cmd/Ctrl+Shift+Z across dashboard editing — moving widgets, resizing, deleting, changing queries. Users get the safety net they expect from every other editor, so experimenting with a layout no longer risks losing work or forcing a manual rebuild from memory.

**Expected outcome**
Fewer accidental destructive edits and support requests to restore dashboards, faster iteration as users edit more freely, and a baseline UX expectation met that currently makes the editor feel less polished than competitors.

**Optional: Key user stories / use cases**

Start by locating the dashboard editor and its handling for moving, resizing, deleting widgets, and changing queries; the issue does not name files or tests. Review how edits are represented before deciding how undo and redo should span those actions. Done means Cmd/Ctrl+Z and Cmd/Ctrl+Shift+Z reliably restore and reapply dashboard edits.

Written by the indexing model from the issue text.