fix: remove RCE vector from admin update endpoint.

The POST /api/admin/update endpoint ran git pull, npm install, and npm run build via execSync, potentially giving any compromised admin account full code execution on the host in case repository is compromised. TREK ships as a Docker image so runtime self-updating is unnecessary.
- Remove the /update route and child_process import from admin.ts
- Remove the installUpdate API client method
- Replace the live-update modal with an info-only panel showing docker pull instructions and a link to the GitHub release
- Drop the updating/updateResult state and handleInstallUpdate handler

client/src/api/client.ts

@@ -163,7 +163,6 @@ export const adminApi = {
   addons: () => apiClient.get('/admin/addons').then(r => r.data),
   updateAddon: (id: number | string, data: Record<string, unknown>) => apiClient.put(`/admin/addons/${id}`, data).then(r => r.data),
   checkVersion: () => apiClient.get('/admin/version-check').then(r => r.data),
-  installUpdate: () => apiClient.post('/admin/update', {}, { timeout: 300000 }).then(r => r.data),
   getBagTracking: () => apiClient.get('/admin/bag-tracking').then(r => r.data),
   updateBagTracking: (enabled: boolean) => apiClient.put('/admin/bag-tracking', { enabled }).then(r => r.data),
   packingTemplates: () => apiClient.get('/admin/packing-templates').then(r => r.data),