CLI: add health probe command

docs/mac/health.md

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+# Health Checks on macOS
+
+How to see whether the WhatsApp Web/Baileys bridge is healthy from the menu bar app.
+
+## Menu bar (planned)
+- Status dot expands beyond “relay running” to reflect Baileys health:
+  - Green: linked + socket opened recently.
+  - Orange: connecting/retrying.
+  - Red: logged out or probe failed.
+- Secondary line reads "Web: linked · auth 12m · socket ok" or shows the failure reason.
+- "Run Health Check" menu item triggers an on-demand probe.
+
+## Settings (planned)
+- General tab gains a Health card showing: linked E.164, auth age, session-store path/count, last check time, last error/status code, and buttons for Run Health Check / Reveal Logs / Relink.
+- Uses a cached snapshot so the UI loads instantly and falls back gracefully when offline.
+
+## How the probe works (planned)
+- App runs `clawdis health --json` via `ShellRunner` every ~60s and on demand. The probe loads creds, attempts a short Baileys connect, and reports status without sending messages.
+- Cache the last good snapshot and the last error separately to avoid flicker; show the timestamp of each.
+
+## Until the UI ships
+- Use the CLI flow in `docs/health.md` (status, heartbeat dry-run, relay heartbeat) and tail `/tmp/clawdis/clawdis.log` for `web-heartbeat` / `web-reconnect`.