feat(remote): host-unreachable banner, manual wake, and native MAC wake-on-LAN

The reactive wake (typing into a session whose host slept) left the state invisible:
nothing told the user the machine was asleep, and with no wake target configured
there was nothing to do about it. Adds:

- RemoteHost.wakeMac (comma-separated) - Codeman builds and broadcasts the magic
  packet itself (UDP port 9), so the common case needs no external script. The
  existing wakeCommand stays as the explicit override.
- GET /api/sessions/:id/reachability - probes (throttled, cached, and it never
  wakes) and reports HOW the host can be woken, or that nothing is configured.
- POST /api/sessions/:id/wake - wakes, waits, reattaches the pane and flushes
  buffered input; 400 with a routable message when no target is configured.
- The amber host-unreachable banner + its 'Wake' / 'Configure WoL' action, and a
  small config dialog that saves via PUT /api/remote-hosts/:id.
- RemoteWakeDeps.resolveRemote: host config is re-resolved for LIVE sessions
  (throttled + cached), so saving the dialog takes effect without a restart.

src/web/public/panels-ui.js

@@ -92,6 +92,9 @@ Object.assign(CodemanApp.prototype, {
   _onRemoteSessionReconnected(data) {
     const id = this.getShortId(data.sessionId);
     this.showToast(`Remote session ${id} reconnected`, 'success');
+    // A successful reattach (the wake flow's own, or the watcher's) means the host is
+    // back: drop the "unreachable" banner without waiting out the poll interval.
+    if (this.activeSessionId === data.sessionId) this._pollHostReachability?.(true);
   },
 
   _onRemoteReconnectExhausted(data) {