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)