approve_node never rotates an existing key; node update-check endpoint; real Update Node button (node-26#14, #15)

- approve_node: reuses node_keys/{id}.api_key when one exists (still
  re-syncs dynsec with it, still never overwrites node_keys). Re-clicking
  Approve can no longer lock a live node out. Reissue stays explicit.
- POST /nodes/{id}/request-update (admin): sets update_requested_at on the
  node doc AND sends MQTT node_update best-effort, so offline/locked-out
  nodes still get it.
- POST /nodes/{id}/update-check (node, inline auth: Bearer api_key for THAT
  node or X-Pickup-Secret): host updater's HTTPS check-in. Returns only
  update_requested_at; records updater_last_check_at / sha / applied result.
  Unknown node -> 401 (no node_id oracle). C2 cannot name a ref, image or
  command.
- Frontend: "Update Node Software" (admin only) calls request-update, honest
  confirm text; node page shows updater check-in and last update state.

Tests: tests/test_node_provisioning.py (12).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-frontend/app/nodes/[id]/page.tsx

@@ -146,6 +146,32 @@ export default function NodeDetailPage() {
     }
   }
 
+  async function handleRequestUpdate() {
+    if (
+      !confirm(
+        "Update this node's software?\n\n" +
+          "The node pulls the latest release it was installed to track and recreates its containers " +
+          "(radio capture pauses for about a minute). An online node starts within seconds; an offline " +
+          "or locked-out node picks it up on its next check-in (up to ~15 minutes). Nodes installed " +
+          "before the host updater existed need install.sh re-run once.",
+      )
+    )
+      return;
+    setSending(true);
+    try {
+      const r = await c2api.requestNodeUpdate(id);
+      alert(
+        r.mqtt_sent
+          ? "Update requested. The node should restart within a minute."
+          : "Update requested. The node is not reachable over MQTT right now; it will update on its next HTTPS check-in.",
+      );
+    } catch (err) {
+      alert(err instanceof Error ? err.message : "Update request failed.");
+    } finally {
+      setSending(false);
+    }
+  }
+
   async function handleApprove() {
     setApproving(true);
     try {
@@ -251,6 +277,15 @@ export default function NodeDetailPage() {
           ["System",    system?.name ?? "Unassigned"],
           ["Location",  `${node.lat}, ${node.lon}`],
           ["Last Seen", node.last_seen ? new Date(node.last_seen).toLocaleString() : "never"],
+          ["Updater Check-in", node.updater_last_check_at ? new Date(node.updater_last_check_at).toLocaleString() : "never"],
+          ...(node.update_requested_at
+            ? [[
+                "Last Update",
+                node.update_applied_at && node.update_applied_at >= node.update_requested_at
+                  ? `${node.update_result === "failed" ? "FAILED" : "applied"} ${new Date(node.update_applied_at).toLocaleString()}`
+                  : `requested ${new Date(node.update_requested_at).toLocaleString()} — pending`,
+              ]]
+            : []),
           ["Configured", node.configured ? "Yes" : "No"],
           ["Node Type", node.node_type ?? "fixed"],
           ...(node.node_type !== "portable" ? [["Enforce Timeout", node.enforce_override_timeout ? "Yes" : "No"]] : []),
@@ -302,17 +337,15 @@ export default function NodeDetailPage() {
         >
           Restart OP25
         </button>
-        <button
-          disabled={sending}
-          onClick={() => {
-            if (confirm("Restart the node container to apply any pulled image updates?")) {
-              sendCommand("node_update");
-            }
-          }}
-          className="px-4 py-2 bg-gray-800 hover:bg-gray-700 text-gray-300 rounded-lg text-sm font-mono transition-colors disabled:opacity-50"
-        >
-          Update Node
-        </button>
+        {isAdmin && (
+          <button
+            disabled={sending}
+            onClick={handleRequestUpdate}
+            className="px-4 py-2 bg-gray-800 hover:bg-gray-700 text-gray-300 rounded-lg text-sm font-mono transition-colors disabled:opacity-50"
+          >
+            Update Node Software
+          </button>
+        )}
         <button
           onClick={() => setShowDiscordJoin(true)}
           className="px-4 py-2 bg-gray-800 hover:bg-gray-700 text-gray-300 rounded-lg text-sm font-mono transition-colors"