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/services/nats.service.ts

@@ -79,4 +79,12 @@ export class NatsService implements OnModuleInit, OnModuleDestroy {
       timestamp: new Date().toISOString(),
     });
   }
+
+  /** Publish an Oxide install command to a specific license's companion agent */
+  async sendOxideInstallCommand(licenseId: string): Promise<void> {
+    await this.publish(`corrosion.${licenseId}.cmd.oxide`, {
+      action: 'install_oxide',
+      timestamp: new Date().toISOString(),
+    });
+  }
 }