CL-7228 surface presence connection loss in the UI

[TheGreatAxios]

CL-7228 surface presence connection loss.

Fixes CL-7228

[TheGreatAxios]

Fixes CL-7228

[TheGreatAxios]

Self-review

Verdict: the presence disconnect/degraded-caption plumbing is correct end-to-end (client onRecovered API → hook state machine → canvas pane caption) and matches existing patterns in the file (ref-based options, exactOptionalPropertyTypes-safe spreads). No defects found; nothing needed fixing.

• DISMISSED: onRecovered fires on every successful join/heartbeat, not only after a prior failure (e.g. first join). Checked call sites — consumers only react to the ok→degraded transition via consecutiveFailuresRef, so the extra no-op recoveries are harmless.
• DISMISSED: trailing prop on CanvasPaneHeader could in principle collide with another trailing consumer. Checked ArtifactCanvasPane — no other trailing usage in that pane, no conflict.
• DISMISSED: principalId carried through a ref rather than an effect dependency, so a principal change won't reconnect. Checked — this mirrors the existing onSaved ref pattern in the same hook (comment explains only doc identity should reconnect), consistent with prior art.
• DISMISSED: docs.md rewrite claims chat-page presence moved to chat.presence SSE (CL-6328) and no longer uses @corbits/presence. Verified via grep — chat-page.tsx has zero references to presence/usePresenceRoom, so the doc update is accurate.

Targeted tests run:

• bun test test/use-presence-room.test.tsx test/canvas-column.test.tsx (apps/web) — 19 pass, 0 fail
• bun test src/client.test.ts (packages/presence) — 27 pass, 0 fail
• bun run typecheck — clean

[linear-code]

CL-7228