feat(KB-332): rename task prefix from KB to FN and branches from kb/ to fusion/

- Change default task prefix from KB to FN across all packages

- Rename branch naming pattern from kb/{id} to fusion/{id}

- Update all test assertions and fixtures to use new prefixes

- Add changeset for the breaking change

- Resolve merge conflicts in TaskCard.test.tsx touch gesture tests

packages/dashboard/app/components/SubtaskBreakdownModal.test.tsx

@@ -38,7 +38,7 @@ describe("SubtaskBreakdownModal", () => {
       streamHandlers = handlers;
       return { close: vi.fn(), isConnected: () => true };
     });
-    mockCreateTasksFromBreakdown.mockResolvedValue({ tasks: [{ id: "KB-101" }, { id: "KB-102" }] });
+    mockCreateTasksFromBreakdown.mockResolvedValue({ tasks: [{ id: "FN-101" }, { id: "FN-102" }] });
     mockCancelSubtaskBreakdown.mockResolvedValue(undefined);
     vi.stubGlobal("confirm", vi.fn(() => true));
   });