fix(api): use instance_id in deleteCloudRuntimeNode body

Fleet API requires instance_id, not id. Fixes 'instance_id is required' error.

MUL-2510

Co-authored-by: multica-agent <github@multica.ai>

packages/core/api/client.test.ts

@@ -248,7 +248,7 @@ describe("ApiClient", () => {
     expect(url).toBe("https://api.example.test/api/cloud-runtime/nodes");
     expect(opts).toMatchObject({
       method: "DELETE",
-      body: JSON.stringify({ id: "node-abc-123" }),
+      body: JSON.stringify({ instance_id: "node-abc-123" }),
     });
     expect((opts.headers as Record<string, string>)["Content-Type"]).toBe(
       "application/json",

packages/core/api/client.ts

@@ -872,7 +872,7 @@ export class ApiClient {
   async deleteCloudRuntimeNode(nodeId: string): Promise<void> {
     await this.fetchRaw("/api/cloud-runtime/nodes", {
       method: "DELETE",
-      body: JSON.stringify({ id: nodeId }),
+      body: JSON.stringify({ instance_id: nodeId }),
       extraHeaders: { "Content-Type": "application/json" },
     });
   }