feat(server-mode): pane presence and typing audit (sharing phase 4)

A pane's tab shows the other people who have it open (pane-presence.js,
in memory, fed by the /ws-pty attach; GET /api/lanes/:id/presence and the
pane_presence broadcast to the owner and full collaborators) and says
"Billed to <name>" for a pane a collaborator opened (startedBy on the run).
The first real keystroke of each attach into a shared workspace's pane by
anyone but its owner is audited as `type into <run id>` (mouse, focus and
terminal replies to tmux do not count). The pty socket now pings, so a
vanished browser is ended at the next re-check and leaves the presence list.

CLAUDE.md

@@ -1,6 +1,6 @@
 # Claude Code Working Guide
 
-_Last synced: v2.8.77+ (2026-11-06) — sharing: collaborators pay for their own runs; one session can be shared._ A change that makes any statement in this file, `AGENTS.md`, or a README wrong — a moved path, a new or changed extension point, a retired rule — updates that file in the same change-set and bumps this marker. **Bump = replace the version/date and a ≤ 1-line summary; never append a changelog here** — details belong in the commit message and `docs/`, because this whole file is loaded into every session.
+_Last synced: v2.8.77+ (2026-11-06) — sharing: payer billing, one-session shares, pane presence + typing audit._ A change that makes any statement in this file, `AGENTS.md`, or a README wrong — a moved path, a new or changed extension point, a retired rule — updates that file in the same change-set and bumps this marker. **Bump = replace the version/date and a ≤ 1-line summary; never append a changelog here** — details belong in the commit message and `docs/`, because this whole file is loaded into every session.
 
 ## Project mission
 - Maintain a reliable local-first dashboard for Claude Code session monitoring.