fix(KB-600): remove duplicate mockedGenerateWorktreeName declaration in executor tests

- Remove redundant const mockedGenerateWorktreeName declaration
- Duplicate was causing potential confusion in worktree naming tests
- No functional changes, test cleanup only

packages/engine/src/executor.test.ts

@@ -381,8 +381,6 @@ describe("TaskExecutor worktree naming", () => {
     ...(worktree ? { worktree } : {}),
   });
 
-  const mockedGenerateWorktreeName = vi.mocked(generateWorktreeName);
-
   beforeEach(() => {
     vi.clearAllMocks();
     mockedExistsSync.mockReturnValue(false);