feat(quick-start): persist agent conversations

[xyh202131]

Summary

• persist each Quick Start agent conversation against its workflow run
• restore the saved conversation when reopening /quick-start/:runId, with localStorage migration and offline fallback
• merge dirty local and remote snapshots with optimistic versioning, idempotent retries, and first-write race handling
• expose the conversation contract in OpenAPI and cover the full frontend/backend flow

Verification

• npm test — 1268 passed
• npm run typecheck — passed
• npm run build — passed
• uv run ruff check . — passed
• uv run pytest tests/test_quick_start_conversation_service.py tests/test_workflow_run_api.py -q — 30 passed
• uv run pytest -q — 1865 passed, 14 skipped, 1 known pre-existing failure in test_ai_chat_scans_text_but_not_image_url because the installed OpenAI package is missing a beta realtime module

[vercel]

Deployment failed for project windup with the following error:

Resource is limited - try again in 24 hours (more than 100, code: "api-deployments-free-per-day").

Learn More: https://vercel.com/huyan-s-projects1?upgradeToPro=build-rate-limit

[github-actions]

⚠️ @xyh202131，此 PR 尚未关联 issue。请在 PR 描述中使用 Closes #123 等关闭关键字；更新描述后，此提醒将自动标记为已解决。

[codecov]

Codecov Report

❌ Patch coverage is 81.84818% with 55 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
frontend/src/pages/quick-start/index.tsx	76.47%	15 Missing and 25 partials ⚠️
...dup_app/server/quick_start_conversation/service.py	80.95%	8 Missing ⚠️
...ntend/src/entities/quick-start-conversation/api.ts	80.00%	2 Missing and 3 partials ⚠️
...ackages/app/src/windup_app/web/api/workflow_run.py	95.91%	2 Missing ⚠️

@@            Coverage Diff             @@
##             main     #837      +/-   ##
==========================================
- Coverage   86.47%   86.46%   -0.02%     
==========================================
  Files         297      301       +4     
  Lines       22355    22615     +260     
  Branches     3402     3443      +41     
==========================================
+ Hits        19331    19553     +222     
- Misses       2074     2096      +22     
- Partials      950      966      +16     

Flag	Coverage Δ
backend	91.46% <90.74%> (-0.01%)	⬇️
frontend	80.54% <76.92%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ckend/packages/app/src/windup_app/bootstrap/app.py	95.72% <100.00%> (+0.03%)	⬆️
...up_app/server/quick_start_conversation/__init__.py	100.00% <100.00%> (ø)
...indup_app/server/quick_start_conversation/model.py	100.00% <100.00%> (ø)
...ackages/app/src/windup_app/web/api/workflow_run.py	98.43% <95.91%> (-1.57%)	⬇️
...ntend/src/entities/quick-start-conversation/api.ts	80.00% <80.00%> (ø)
...dup_app/server/quick_start_conversation/service.py	80.95% <80.95%> (ø)
frontend/src/pages/quick-start/index.tsx	83.87% <76.47%> (-0.17%)	⬇️

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[fennoai]

Reviewed the complete fixed diff for the Quick Start conversation persistence contract, including backend authorization and optimistic locking, frontend local/server reconciliation, migration/offline fallback, tests, and OpenAPI synchronization. I found no actionable correctness, security, performance, or compatibility regression introduced by this PR. Python compilation and git diff --check pass; the focused runtime suites were not runnable in this workspace because uv and the frontend test dependencies are unavailable.