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>

backend-nest/src/modules/servers/servers.service.ts

@@ -103,4 +103,12 @@ export class ServersService {
     await this.natsService.sendDeployCommand(licenseId, { ...dto });
     return { message: 'Deployment started' };
   }
+
+  /**
+   * Install Oxide/uMod via companion agent
+   */
+  async installOxide(licenseId: string) {
+    await this.natsService.sendOxideInstallCommand(licenseId);
+    return { message: 'Oxide installation started' };
+  }
 }