Adds Ctrl+N toggle to filter sessions by named-only vs all in the /resume picker.
- Add NameFilter type and filtering logic to session-selector-search.ts
- Add toggleSessionNamedFilter app keybinding (default: ctrl+n)
- Show Name: All/Named state in header
- Empty state mentions toggle keybinding as escape hatch
- Export hasSessionName() to avoid duplication
Co-authored-by: warren <warren.winter@gmail.com>
Adds 'Threaded' as a new sort mode (now default) that displays sessions
in a tree structure based on parent-child relationships. The tree is
sorted by root session's modified date. Other sort modes (Recent, Fuzzy)
continue to show flat lists.
Sort mode cycles: Threaded -> Recent -> Fuzzy -> Threaded
