Make restore-from-standby actually work, not just look wired

Two gaps found testing this live from the standby:

1. restore.html's "Restore on This Server" was checked by default
   regardless of RUNNING_ON_MAIN_SERVER — on the standby that option is
   nonsensical (no local cluster/kubectl at all) and restore_start()
   would have just tried and failed confusingly. Now: that radio is
   disabled with an explanatory note when not on the main server,
   "External Machine" is checked instead and pre-filled with the tunnel
   details (localhost:2224, contabo-key) so restoring from the standby
   just targets the real main server without the user having to know
   any of that. Added a matching server-side guard in restore_start()
   for target=='local' + not RUNNING_ON_MAIN_SERVER (defense in depth —
   the UI already prevents it, this catches a direct API call too).
   Also fixed refreshSystemMetrics() in platform.js, which would have
   overwritten the disabled option's label with the (now-correct, see
   previous commit) main-server hostname — looking like a working local
   target when it isn't.

2. sync-standby-platform.sh only ever mirrored platform/ — but
   restore_start() references /root/CloudOps/backup/restore-k8s-apps.sh
   as a fixed absolute path to scp to the remote target, and that
   directory never existed on the VM at all. Every restore attempt from
   the standby failed immediately with "restore-k8s-apps.sh not found",
   regardless of target. Now mirrors /root/CloudOps/backup/ too.

Verified end-to-end for real: triggered a restore of frappe/erpnext from
the standby's actual web UI (target=remote, localhost:2224) — connected
over the tunnel, copied the backup archive + script to the main server,
ran restore-k8s-apps.sh there, scaled the deployment down/up, restored
the DB. Confirmed after: 740 tables in the DB, /api/method/ping
responding on the live pod. Not a dry run — a real restore, actually
initiated from the standby machine.

platform/templates/pages/restore.html

@@ -63,26 +63,37 @@
 
     <div class="form-section">
       <div class="form-section-title">STEP 2 — SELECT RESTORE TARGET</div>
+      {% if not running_on_main_server %}
+      <div style="margin-bottom:12px;padding:10px 14px;background:rgba(245,158,11,0.08);
+        border:1px solid rgba(245,158,11,0.25);border-radius:8px;font-size:12px;color:var(--yellow);">
+        <i class="fas fa-triangle-exclamation"></i>
+        Running as the standby — there's no local cluster here to restore into.
+        "External Machine" is pre-filled to reach the real main server over the standby's
+        SSH tunnel; only change these if you actually mean a different target.
+      </div>
+      {% endif %}
       <div class="radio-group">
-        <label class="radio-card">
-          <input type="radio" name="restore_target" value="local" checked onchange="toggleRemoteFields()">
-          <div class="radio-body"><span class="radio-icon">🎯</span><div><div class="radio-label">Restore on This Server</div><div class="radio-desc" id="this-server-desc">Loading hostname…</div></div></div>
+        <label class="radio-card{% if not running_on_main_server %} disabled{% endif %}">
+          <input type="radio" name="restore_target" value="local"
+            {% if running_on_main_server %}checked{% else %}disabled{% endif %}
+            onchange="toggleRemoteFields()">
+          <div class="radio-body"><span class="radio-icon">🎯</span><div><div class="radio-label">Restore on This Server</div><div class="radio-desc" id="this-server-desc">{% if running_on_main_server %}Loading hostname…{% else %}Not available on the standby{% endif %}</div></div></div>
         </label>
         <label class="radio-card">
-          <input type="radio" name="restore_target" value="remote" onchange="toggleRemoteFields()">
+          <input type="radio" name="restore_target" value="remote" {% if not running_on_main_server %}checked{% endif %} onchange="toggleRemoteFields()">
           <div class="radio-body"><span class="radio-icon">📡</span><div><div class="radio-label">External Machine</div><div class="radio-desc">via SSH — any IP</div></div></div>
         </label>
       </div>
 
-      <div id="remote-fields" style="display:none; margin-top:16px; max-width:560px;">
+      <div id="remote-fields" style="display:{% if running_on_main_server %}none{% else %}block{% endif %}; margin-top:16px; max-width:560px;">
         <div class="form-row">
           <div class="form-group">
             <label class="form-label">TARGET IP</label>
-            <input type="text" id="remote-ip" class="form-input" placeholder="192.168.x.x or IP">
+            <input type="text" id="remote-ip" class="form-input" placeholder="192.168.x.x or IP" value="{{ tunnel_remote_ip if not running_on_main_server else '' }}">
           </div>
           <div class="form-group" style="max-width:100px;">
             <label class="form-label">SSH PORT</label>
-            <input type="text" id="remote-port" class="form-input" value="22">
+            <input type="text" id="remote-port" class="form-input" value="{{ tunnel_remote_port if not running_on_main_server else '22' }}">
           </div>
           <div class="form-group" style="max-width:120px;">
             <label class="form-label">SSH USER</label>