feat(console): operator participant mode — agents can reply to you

[Lanzelot1]

What

Sending from cotal console was one-way: the console joins as an invisible observer (registerPresence:false) with no inbox (consume:false), so an agent's DM reply to the operator had no consumer to land in and expired unread. Channel posts already round-tripped (agents reply in-channel, the tap shows it); DMs/:call/:ask didn't.

Now, on the operator's first send, the console upgrades the observer in place (no rebuild, no provisioning, no manager):

• Presence — a new CotalEndpoint.startPresence() registers the operator as a role:"operator" peer, so agents see it on the roster and can reply. Clean offline leave on exit (reuses the existing stop path).
• Receive — MeshView reveals the DM lens and captures the operator's own inbox. On an auth mesh (chat-narrowed tap) it opens a second tap scoped to inst.<selfId>.>; on an open mesh the whole-space tap already covers it (so no second tap — avoids a double-count). A best-effort one-shot backfill catches a reply that raced activation.
• Outbound DMs are recorded locally (auth path) so a thread shows both sides.

Gating / reach: canWrite-gated, so a pure-watch session never registers (stays invisible). It works where the console can actually send — an open mesh (bare) or an auth mesh with a capable --creds. Under the auth-default read-only god-view cred the console can't send at all, so participant mode never activates there; full auth-default participation would need a dedicated participant cred profile (future work, deliberately out of scope to keep this minimal and not touch the core cred matrix).

Stacked on #200 (feat/console-control) — retarget to main after it lands.

Verified

• pnpm typecheck + pnpm test + smoke:view clean.
• Live end-to-end (open broker + a stub agent that acks any DM): before activation the operator is off the roster; after a :dm, it registers (the stub sees it), the agent's ack reaches the operator's DM lens as a two-sided thread, and there's exactly one distinct outbound (no double-count). 5/5.
• tmux click-through: :dm @stub hi there → operator joins the roster as an endpoint peer, the feed shows the reply, the DM lens shows user → stub / stub → user: ack; on q the operator deregisters cleanly (only the agent remains live).

Core change

One small, generic method — CotalEndpoint.startPresence() (post-construction presence + heartbeat, idempotent) + making doRegister mutable + a scoped inboxHistory(selfId). Everything else is console/MeshView.