/resume should include background sessions (or add a separate picker for them)

Currently Claude Code has two separate UIs for sessions:

• /resume shows only interactive sessions. Background sessions (started via /bg or claude --bg) never appear in the picker — not even after their job entry has been deleted via Ctrl+X Ctrl+X in claude agents.
• claude agents shows only sessions that have an active record in ~/.claude/jobs/<id>/. After Ctrl+X Ctrl+X the session disappears from there too.

Meanwhile the full JSONL transcript is still on disk at ~/.claude/projects/<encoded-cwd>/<full-session-id>.jsonl, and the session can be revived — but only by knowing the full session id and running from the shell:

claude --resume <full-session-id>

This is awkward: to return to a previously-existing background session you have to drop into the filesystem, grep transcripts and copy a UUID, instead of just picking it from a list.

Proposal — one of:

1. Add a toggle to /resume (e.g. Ctrl+G — "show background / orphaned sessions") so the picker also lists them.
2. Or add a separate command — e.g. /sessions — listing every JSONL under projects/ regardless of whether a jobs/ entry exists.
3. Or add an "archived / orphaned" tab to claude agents for sessions whose transcript still exists but whose job record has been deleted.

Any of these would close the gap: right now a background session is effectively unreachable from any UI after Ctrl+X Ctrl+X, even though the data is physically present on disk.

Repro

1. Start a background session (/bg or claude --bg), let it finish.
2. In claude agents, select it and press Ctrl+X Ctrl+X (delete).
3. Open /resume — the session is not listed.
4. Open claude agents — also not listed.
5. The transcript ~/.claude/projects/<encoded-cwd>/<full-id>.jsonl is still on disk and claude --resume <full-id> opens it fine.

Environment

• Claude Code CLI version: 2.1.140
• Platform: Linux