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>