fix(backend): advanced-search e2eのフレーキーなoff-by-oneを堅牢化

[4ster1sk]

What

packages/backend/test/e2e/advanced-search.ts の fullIndexNote E2E準備処理を堅牢化しました（テストのみの変更、本体ロジックの変更なし）。

• 2200件の notes/create 連打をステータス検証付きに変更し、失敗時は最大3回リトライ（失敗箇所の i と最終レスポンスをエラーメッセージに含める）
• 投稿後の users/show.notesCount 確認を単発 strictEqual から60秒ポーリングに変更

Why

opensearch-e2e でフレーキーな失敗が発生していました：

AssertionError: Expected 2200 notes, but got 2199
at test/e2e/advanced-search.ts:72

連打中の1件の過渡失敗が無チェックの post() で黙って握りつぶされ、そのまま off-by-one になるのが原因と判断しました。notesCount の反映遅延も単発assertでは吸収できませんでした。

Additional info (optional)

• 検証済み: pnpm build、pnpm --filter backend typecheck、pnpm --filter backend eslint 通過
• 未検証: OpenSearch実機での test:e2e:opensearch（要DB/Redis/OpenSearchのためCIでの確認が必要）
• ベース: yojo-art/1.11.x、他ファイル・locale・migration・API定義の変更なし

Checklist

• コントリビューションガイドを読みました( Read the contribution guide)
• ローカル環境で動作しました(Test working in a local environment)
• (必要なら)CHANGELOG_YOJO.mdの更新((If needed) Update CHANGELOG_YOJO.md)
• (必要なら)テストの追加((If possible) Add tests)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 23.24%. Comparing base (7f6293f) to head (a8e3845).
⚠️ Report is 6 commits behind head on 1.11.x.

Additional details and impacted files

@@            Coverage Diff             @@
##           1.11.x    #1360      +/-   ##
==========================================
- Coverage   23.68%   23.24%   -0.44%     
==========================================
  Files        1269     1267       -2     
  Lines       49135    48922     -213     
  Branches    14471    14433      -38     
==========================================
- Hits        11637    11373     -264     
- Misses      29599    29636      +37     
- Partials     7899     7913      +14     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

Backend memory usage comparison

Before GC

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	432.14 MB	457.82 MB	+25.67 MB	+5.94%
VmHWM	432.14 MB	457.82 MB	+25.67 MB	+5.94%
VmSize	3213.46 MB	3238.93 MB	+25.47 MB	+0.79%
VmData	2014.77 MB	2040.63 MB	+25.86 MB	+1.28%

After GC

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	432.15 MB	457.62 MB	+25.47 MB	+5.89%
VmHWM	432.15 MB	457.68 MB	+25.53 MB	+5.90%
VmSize	3213.79 MB	3238.68 MB	+24.89 MB	+0.77%
VmData	2015.10 MB	2040.38 MB	+25.28 MB	+1.25%

After Request

Metric	base (MB)	head (MB)	Diff (MB)	Diff (%)
VmRSS	431.83 MB	457.78 MB	+25.94 MB	+6.00%
VmHWM	432.27 MB	457.93 MB	+25.66 MB	+5.93%
VmSize	3213.71 MB	3238.52 MB	+24.81 MB	+0.77%
VmData	2015.02 MB	2040.22 MB	+25.19 MB	+1.25%

⚠️ Warning: Memory usage has increased by more than 5%. Please verify this is not an unintended change.

See workflow logs for details

[github-actions]

このPRによるapi.jsonの差分
差分はありません。
Get diff files from Workflow Page