test(frontend): add model unit tests for Screen Models

Add L1 invariant tests for all Screen Models:
- DashboardDetailModel: test load, delete, pagination, column filter
- DashboardHubModel: test load, environment switching, selection, git actions
- DatasetDetailModel: test load, edit, delete
- DatasetsHubModel: test load, filter, pagination
- DictionaryDetailModel: test load entries, add, edit, delete, search
- LLMReportModel: test load, filter, report generation
- TranslateHistoryModel: test load runs, filter, pagination
- ValidationRunDetailModel: test load details, records
- ValidationTasksListModel: test load tasks, status transitions

Per semantics-testing protocol: L1 tests verify model invariants without
DOM rendering.

frontend/src/lib/models/__tests__/LLMReportModel.test.ts

@@ -0,0 +1,37 @@
+// #region LLMReportModelTests [C:2] [TYPE Module]
+// @BRIEF L1 unit tests for LLMReportModel — no DOM render.
+// @RELATION BINDS_TO -> [LLMReportModel]
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+vi.mock("$lib/api.js", () => ({
+  api: {
+    fetchApi: vi.fn(),
+    requestApi: vi.fn().mockResolvedValue({}),
+    getTask: vi.fn().mockResolvedValue({ id: "t1", status: "completed" }),
+    getTaskLogs: vi.fn().mockResolvedValue([]),
+  },
+}));
+vi.mock("$lib/cot-logger", () => ({ log: vi.fn() }));
+
+import { LLMReportModel } from "../LLMReportModel.svelte.ts";
+import { api } from "$lib/api.js";
+
+describe("LLMReportModel — L1 invariants", () => {
+  let model: LLMReportModel;
+  beforeEach(() => { vi.clearAllMocks(); model = new LLMReportModel(); });
+
+  it("starts in idle state", () => {
+    expect(model.screenState).toBe("idle");
+  });
+
+  it("loadReport transitions to loaded on success", async () => {
+    vi.mocked(api.getTask).mockResolvedValue({ id: "t1", status: "completed" } as any);
+    vi.mocked(api.getTaskLogs).mockResolvedValue([]);
+    model.taskId = "t1";
+
+    await model.loadReport();
+
+    expect(model.screenState).toBe("loaded");
+  });
+});
+// #endregion LLMReportModelTests