Checkpoint & Task Management

Priority: P1

CLI-side snapshot service is fully implemented (packages/opencode/src/snapshot/). Extension has a settings toggle. What's missing is the management UI.

Remaining Work

• Checkpoint restore dialogs
• Checkpoint navigation menu / timeline
• Diff viewing between checkpoints
• "See New Changes" buttons to view git diffs for completed tasks
• Integration with CLI session undo/redo/fork operations
• Consider reusing kilo-ui's MessageNav component
• Evaluate whether CLI session undo/redo/revert maps to Kilo's checkpoint model or if extension needs its own git-based implementation