UX: /resume should distinguish between favorites (named sessions) and full history

Description

The in-session /resume slash command silently filters to only show named sessions (those with a custom-title or agent-name). When no named sessions exist, it falls back to showing all sessions. This creates confusing behavior where sessions seem to disappear.

Current behavior

• 0 named sessions → /resume shows all sessions
• 1+ named sessions → /resume shows only named sessions
• No indication that filtering is happening
• claude --resume from terminal always shows all sessions

Suggestion

Make the in-session /resume picker explicit about the two modes:

• Favorites / named sessions — quick access to renamed or agent-named sessions
• Full history — all sessions, like claude --resume from terminal

Either show both sections in the picker, or add a keyboard shortcut to toggle between them (similar to how claude --resume has Ctrl+B to toggle branch filtering).

Environment

• Claude Code CLI (terminal)
• macOS