[Dhruv-Sharma29]

Closes #462

Problem

Work Mode let you accept an AI result, but the Work panel had no way to undo it.

• Active document: editor Undo (Cmd/Ctrl+Z) could step back over the AI edit, but nothing in Work Mode offered this.
• Open project: accepting a proposal writes several tabs through React state, outside any single Monaco model, so editor Undo could not revert it at all.

Changes

Active-document Work

• After a result is applied, the Work tab shows an Undo AI Changes button.
• It restores the pre-Work text through the existing applyWorkEdit path, as one undoable editor edit. Editor Undo can then bring the AI result back.
• If the document was edited after the AI result was applied, it refuses and points you to editor Undo instead. It never overwrites your later typing. The freshness check reuses isWorkResultFresh.

Project Work

• Before accepting a proposal, captureProjectWorkUndo snapshots every tab the change touches.
• Undo accepted changes in the project review calls revertProjectWork, which:
  • restores each modified tab's previous content and dirty state;
  • closes the tabs that the result opened;
  • leaves alone any tab that was edited after accepting, or a new file that was already saved, and lists those files in the status message;
  • keeps a tab dirty if its AI content was saved, because the file on disk no longer matches the restored text.
• Switching projects clears the undo record.

Files

• frontend/src/lib/project-work-undo.mjs: the capture and revert logic (pure functions, easy to test)
• useProjectWork, useEditor (revertProjectChanges), useAIActions (undoWork, canUndoWork), AIPanel, ProjectWorkReview: wiring and buttons

Testing

• New tests/project-work-undo.test.mjs covers: reverting edits and closing opened tabs, never discarding later user edits, and saved results and saved new files.
• npm test (165 pass), npx tsc --noEmit, npm run lint, npm run build all pass.
• I didn't test the full AI round trip by hand, because it needs a configured AI provider.

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