feat(FN-4044): restore github tracking patch persistence

Restored GitHub tracking patch persistence in the core store with matching test coverage in the task detail and routes tasks ops suites, plus documentation for the repaired flow.

Fusion-Task-Id: FN-4044

packages/dashboard/app/components/__tests__/TaskDetailModal.inline-editing-and-integrations.test.tsx

@@ -2225,7 +2225,23 @@ describe("TaskDetailModal", () => {
     it("shows create tracking issue action for enabled but unlinked tasks outside editable columns", async () => {
       const { updateTask } = await import("../../api");
       const mockUpdate = vi.mocked(updateTask);
-      mockUpdate.mockResolvedValueOnce({ id: "FN-001" } as Task);
+      const onTaskUpdated = vi.fn();
+      const addToast = vi.fn();
+      const updatedTask = makeTask({
+        id: "FN-001",
+        column: "done",
+        githubTracking: {
+          enabled: true,
+          issue: {
+            owner: "runfusion",
+            repo: "fusion",
+            number: 77,
+            url: "https://github.com/runfusion/fusion/issues/77",
+            createdAt: "2026-01-01T00:00:00Z",
+          },
+        },
+      });
+      mockUpdate.mockResolvedValueOnce(updatedTask as Task);
 
       render(
         <TaskDetailModal
@@ -2235,7 +2251,8 @@ describe("TaskDetailModal", () => {
           onMoveTask={noopMove}
           onDeleteTask={noopDelete}
           onMergeTask={noopMerge}
-          addToast={noop}
+          onTaskUpdated={onTaskUpdated}
+          addToast={addToast}
         />,
       );
 
@@ -2245,6 +2262,8 @@ describe("TaskDetailModal", () => {
       await waitFor(() => {
         expect(mockUpdate).toHaveBeenCalledWith("FN-001", { githubTracking: { enabled: true } }, undefined);
       });
+      expect(onTaskUpdated).toHaveBeenCalledWith(updatedTask);
+      expect(addToast).toHaveBeenCalledWith("Requested GitHub tracking issue creation", "info");
       expect(screen.queryByLabelText("Enable GitHub tracking")).toBeNull();
     });