feat: Add one-click Oxide/uMod installer — backend + frontend

POST /servers/install-oxide endpoint, NATS bridge for oxide.status,
server store installOxide method, ServerView Install Oxide card with
progress tracker matching the Deploy card pattern.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/stores/server.ts

@@ -64,6 +64,15 @@ export const useServerStore = defineStore('server', () => {
     }
   }
 
+  async function installOxide() {
+    try {
+      await api.post('/servers/install-oxide')
+    } catch (e) {
+      console.error('Failed to start Oxide installation:', e)
+      throw e
+    }
+  }
+
   function updateDeploymentStatus(status: DeploymentStatus) {
     deploymentStatus.value = status
     if (status.stage === 'online' || status.stage === 'failed') {
@@ -94,6 +103,7 @@ export const useServerStore = defineStore('server', () => {
     stopServer,
     restartServer,
     deployServer,
+    installOxide,
     updateDeploymentStatus,
     clearDeploymentStatus,
     updateStats,