v0.169.0: macOS process sandbox, spec rendering fixes, and MCP session improvements

New features

- macOS command sandbox - Added whole-process sandbox support on macOS for safer command execution

Improvements

- Clearer send button - The composer now explains why the send button is disabled (app)
- Safer web tools - WebSearch and FetchUrl now require at least low autonomy before they run

Bug fixes

- Image-only messages - Fixed sending messages that contain only an image
- Plan todos - Plan todo lists are now bounded and the full todo displays correctly
- Wide tables - Wide markdown tables now scroll horizontally
- MCP footer - The MCP status footer now appears immediately
- MCP session notices - MCP status and auth notices now stay scoped to their session instead of leaking into untouched sessions
- Spec rendering - Spec contents now render in the approval details screen, and the spec body shows when the plan heading matches the title
- Update rollback - Hardened the update rollback flow (app)