test(desktop): wait for narrative fixture workbar

[liuxiaocs7]

Summary

Wait for the seeded Git changes panel to become visible before the narrative fixture hands its page to tests. This closes the initialization gap where the fixture could select Review after the usage action had already selected Trace.

Fixes #4968

Verification

• npm exec -- biome check apps/desktop/e2e/fixtures.ts
• npm --workspace @maka/desktop run build:workspace-deps && npm --workspace @maka/desktop run typecheck
• npm exec -w @maka/desktop -- playwright test --config e2e/playwright.config.ts e2e/session-workbar.spec.ts --grep "the composer usage action opens Task trace in the right workbar" --repeat-each=10 (10 passed)
• git diff origin/main...HEAD --check

AI use

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: OpenAI Codex investigated the CI failure, implemented the fixture synchronization, and ran verification. The commit includes the required Generated-by: OpenAI Codex trailer.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No

[me2seeks]

Automated review by OpenAI Codex, operated by me2seeks, at 799c76e2e3bb343f2106ba8bc48d21a6b69fadb2. This is an automated technical assessment, not an independent human review. Approval is submitted at the operator's explicit direction.

No actionable findings. The turn-narrative producer seeds workbarTab=review only after deferred fixture application. Waiting for the localized Git changes region before handing the page to consumers closes the fixture/test ordering race without production synchronization, polling counters, or sleeps.

1. Optimal for the actual problem: Yes; the change addresses the defect at its existing owner.
2. Production code that can be deleted: None identified.
3. Low-quality tests that can be deleted or replaced: None identified.
4. Deeper refactor: No deeper refactor is needed.
5. Ready to merge: Content is ready; merge remains conditional on current required checks and conflict state.
6. Residual risks / verification: Read the exact fixture, seed producer, region copy, and consuming workbar test; required hosted test passed. Did not rerun Electron E2E locally. No protected-area effect identified in this diff.