Add SSH+kubectl remote fallback so the standby actually shows cluster/app health

Two real gaps found after testing the live standby platform:

1. modules/kubernetes.py's in-cluster client (load_incluster_config())
   can only ever work inside the real k8s pod. On the standby it silently
   returned K8S_AVAILABLE=False with zero fallback — Cluster, Containers-
   via-sites, and any cluster/app health data was just empty on that page,
   not erroring, so it was easy to miss. This holds even if the standby
   later runs as a pod on a *local* k3s on that server (per plan for the
   monitoring migration) — in-cluster config there would only ever see
   that local, unrelated cluster, never the main one.

   Fixed by adding an SSH+kubectl remote path to list_pods(), list_
   deployments(), get_ingress_info(), list_deployments_for_namespace(),
   and get_pod_metrics(): when not RUNNING_ON_MAIN_SERVER, each runs
   `kubectl <verb> -o json` on the main server over the tunnel
   (main-to-vm-tunnel.service) instead of using the python client, parses
   the raw (camelCase) JSON directly rather than trying to force it
   through the client-library's snake_case object model, and feeds the
   same _pod_health/_deploy_health/_age_str helpers either way. The
   in-cluster path for the real main-server pod is untouched.

2. get_system_info() called psutil.* unconditionally with no
   RUNNING_ON_MAIN_SERVER awareness at all — on the standby it was
   silently reporting the VM's OWN cpu/mem/disk/hostname mislabeled as
   "system info" (hostname field literally showed the VM's hostname).
   Added _get_main_server_system_info_remote(): SSHes to the main server
   and gathers the same stats via vmstat/free/df/procfs (the main
   server's bare host has no psutil — that's only in this app's own
   container image — so this avoids depending on it being present
   remotely).

Verified end-to-end on the live standby: /api/system now reports the
real main server's hostname/cpu/mem/disk/uptime; /api/cluster reports
real counts (19 pods, 16/16 deployments healthy, 3 degraded, plus live
per-pod metrics via the metrics-server raw API); /api/sites shows real
per-app container/role status. All previously silently empty.

platform/modules/backups.py

@@ -895,8 +895,65 @@ def get_all_stats():
 # SYSTEM INFO (FIXED WITH PSUTIL)
 # ────────────────────────────────────────────────────────────────
 
+def _get_main_server_system_info_remote():
+    """get_system_info()'s equivalent for the standby: the main server's bare
+    host has no psutil (system python3, not this app's container image), so
+    this uses plain coreutils/procps instead — reusing _ssh_main means this
+    genuinely queries the real main server over the tunnel, not the VM
+    itself (the previous unconditional psutil.* calls silently reported the
+    VM's own stats mislabeled as "system info" whenever running as standby)."""
+    fallback = {
+        'cpu_pct': '0', 'memory': 'N/A', 'mem_pct': '0', 'disk': 'N/A',
+        'disk_pct': '0', 'load': 'N/A', 'uptime': 'N/A', 'docker_v': 'N/A',
+        'hostname': 'unreachable',
+    }
+    remote_cmd = (
+        "hostname; "
+        "vmstat 1 2 | tail -1 | awk '{print 100-$15}'; "
+        "free -m | awk 'NR==2{printf \"%d %d %d\\n\", $3, $2, $3*100/$2}'; "
+        "df -BM --output=used,size,pcent / | tail -1 | tr -d 'M%'; "
+        "awk '{printf \"%.2f %.2f %.2f\\n\", $1, $2, $3}' /proc/loadavg; "
+        "awk '{print $1}' /proc/uptime; "
+        "docker --version 2>/dev/null | awk '{print $3}' | tr -d ','"
+    )
+    out, err = _ssh_main(remote_cmd, timeout=15)
+    lines = out.split('\n') if out else []
+    if len(lines) < 7:
+        return fallback
+    try:
+        hostname = lines[0].strip()
+        cpu_pct = lines[1].strip()
+        mem_used_mb, mem_total_mb, mem_pct = lines[2].split()
+        disk_used_mb, disk_total_mb, disk_pct = lines[3].split()
+        load = lines[4].strip()
+        uptime_s = float(lines[5].strip())
+        docker_v = lines[6].strip() or 'N/A'
+
+        days = int(uptime_s // 86400)
+        hours = int((uptime_s % 86400) // 3600)
+        minutes = int((uptime_s % 3600) // 60)
+        uptime = f"{days}d {hours}h {minutes}m" if days > 0 else f"{hours}h {minutes}m"
+
+        return {
+            'cpu_pct':  cpu_pct,
+            'memory':   f"{int(mem_used_mb) / 1024:.1f}G/{int(mem_total_mb) / 1024:.1f}G",
+            'mem_pct':  mem_pct,
+            'disk':     f"{int(disk_used_mb) / 1024:.0f}G/{int(disk_total_mb) / 1024:.0f}G",
+            'disk_pct': disk_pct,
+            'load':     load,
+            'uptime':   uptime,
+            'docker_v': docker_v,
+            'hostname': hostname,
+        }
+    except Exception as e:
+        print(f"[backups] remote system info parse error: {e} (raw: {out!r}, err: {err!r})")
+        return fallback
+
+
 def get_system_info():
     """Get system information using psutil for reliable metrics inside container"""
+    if not RUNNING_ON_MAIN_SERVER:
+        return _get_main_server_system_info_remote()
 
     info = {
         'cpu_pct': '0',