feat(box): passkey fetch, agent key-approval flow, unified lookups, tmux agent UX

- box passkey [show|fetch] (+ muse passkey): documents VM-only passkey
  (/srv/box/passkey.txt, fallback /etc/netvm/passkey.txt on 34.139.37.135),
  probes VM over SSH with graceful fallback; --json supported. No secrets on bl.
- approvals: request_key_approval / check_node_key_request; KEY_APPROVAL status
  surfaced in `box approvals check`; allow/deny resolve + audit to box-ctl.jsonl;
  never auto-approved. New `box approvals request-key <node> --reason`.
- box lookup (summary|fleet|threads|unread|approvals|key|docs) and docs-lookup
  engine with lookup_internal/ database (docs_internal symlink).
- muse-tmux: non-TTY attach falls back to scrollback capture; prune NameError fix.
- box/muse passthrough for tmux/muse/docs; thread list/view alias + prefix resolve.
- Docs: AGENTS.md, AGENT-TOOLING.md, BOX-WEB-SURFACE-GUIDE.md, README.
- Tests: key-approval + passkey tests; sync stale sidechat UUIDs and manifest name.
- .gitignore runtime trackers (subagent-sessions, conversation-nudge-tracker).

.gitignore

@@ -25,3 +25,5 @@ ssl/
 job-scheduler-state.json
 var/
 swarms.json
+subagent-sessions.json
+conversation-nudge-tracker.json