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.controller.ts

@@ -73,4 +73,11 @@ export class ServersController {
   ) {
     return await this.serversService.deployServer(licenseId, dto);
   }
+
+  @Post('install-oxide')
+  @RequirePermission('server.manage')
+  @ApiOperation({ summary: 'Install Oxide/uMod via companion agent' })
+  async installOxide(@CurrentTenant() licenseId: string) {
+    return await this.serversService.installOxide(licenseId);
+  }
 }