feat(nodes): bulk panel self-update with live online indicator

Adds the ability to update node panels to the latest release from the Nodes
page: select online, enabled nodes (checkboxes) and trigger their official
self-updater, or use the per-row Update action. A node whose reported panel
version trails the latest GitHub release is flagged with an 'update available'
tag (compared via lib/panel-version, mirroring the Go isNewerVersion).

Backend: Remote.UpdatePanel calls the node's existing
POST /panel/api/server/updatePanel; NodeService.UpdatePanels fans out over the
selected ids, skipping disabled/offline nodes with a per-node reason; exposed
as POST /panel/api/nodes/updatePanel (documented in endpoints.ts + openapi.json).

The bulk request sends a JSON body, so it sets Content-Type: application/json
explicitly — axios defaults POST to form-urlencoded, which made ShouldBindJSON
fail with 'invalid character i'.

Also reuses the clients-page online cue on the Nodes page: a pulsing green dot
plus green label for an online node. The .online-dot style moved to the shared
styles/utils.css so both pages load it.

Translations for all new node keys added across every language file.

frontend/src/pages/api-docs/endpoints.ts

@@ -777,6 +777,13 @@ export const sections: readonly Section[] = [
           { name: 'id', in: 'path', type: 'number', desc: 'Node ID.' },
         ],
       },
+      {
+        method: 'POST',
+        path: '/panel/api/nodes/updatePanel',
+        summary: 'Trigger the official panel self-updater on each given node (downloads the latest release and restarts). Only enabled, online nodes are updated; offline/disabled ones are reported as skipped. Returns a per-node result list.',
+        body: '{\n  "ids": [1, 2, 3]\n}',
+        response: '{\n  "success": true,\n  "obj": [\n    { "id": 1, "name": "de-1", "ok": true },\n    { "id": 2, "name": "fr-1", "ok": false, "error": "node is offline" }\n  ]\n}',
+      },
       {
         method: 'GET',
         path: '/panel/api/nodes/history/:id/:metric/:bucket',