Tasks: Secondary window polish

• T001 Specify accepted scenarios and native implementation plan.
• T002 Add behavior regression assertions to existing isolated GTK fixtures and establish failure.
• T003 Implement board title layout and overflow navigation.
• T004 Implement compact Worktrees and branch/path hierarchy.
• T005 Implement filtered palette headers and secondary shortcut styling.
• T006 Replace theme orbs with paired application miniatures; strengthen Changes hierarchy.
• T007 Run full verification, review native renders, save selected evidence and update docs.
• T008 Independent standards/spec review; resolve findings; commit, push and open linked PR.

Dependencies: T001 → T002 → T003–T006 → T007 → T008. One writer; no parallel implementation.

Submitted: https://github.com/Lucenx9/signaltty/pull/99