i18n(ja): unify Request Unit (RU) notation

[yahonda]

What is changed, added or deleted? (Required)

"Request Unit (RU)" had two minority variant translations scattered across the corpus — 要求単位 (9 occurrences) and 要求ユニット (3 occurrences) — inconsistent with the dominant, glossary-defined term リクエストユニット (66 existing occurrences, including the glossary.md entry itself: ### リクエストユニット（RU） {#request-unit-ru}).

Unified 13 occurrences across 7 files:

• grafana-resource-control-dashboard.md (3 sites: RRU/WRU descriptions using 要求単位 and 要求ユニット, inconsistent with the RU/WRU-per-query lines in the same list which already correctly say リクエストユニット)
• dashboard/dashboard-resource-manager.md (2 sites)
• releases/release-6.6.0.md, tidb-cloud/architecture-concepts.md, tidb-cloud/manage-serverless-spend-limit.md, tidb-cloud/select-cluster-tier.md (2 sites), tidb-resource-control-ru-groups.md (2 sites)

Which TiDB version(s) do your changes apply to? (Required)

• i18n-ja-release-8.5 (TiDB Japanese documentation for TiDB 8.5 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):

AI agent involvement

• The changes in this PR were primarily made by an AI agent on behalf of the PR author.

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

Summary by CodeRabbit

• Documentation
  • Standardized Japanese terminology for “Request Units (RU)” across resource control, TiDB Cloud, and release documentation.
  • Updated dashboard metric names to English: “Total RU Consumed” and “RU Consumed by Resource Groups.”
  • Clarified TiFlash resource-control guidance by listing flow-control and scheduling guidance for both TiDB and TiDB Cloud variants.
  • Preserved existing metric descriptions, quota values, and reference links.

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[coderabbitai]

📝 Walkthrough

Walkthrough

The pull request standardizes RU terminology across Japanese and English documentation. It also adds TiFlash scheduling guidance to the TiDB Cloud platform section.

Changes

Resource control documentation

Layer / File(s)	Summary
RU terminology alignment dashboard/dashboard-resource-manager.md, grafana-resource-control-dashboard.md, releases/release-6.6.0.md, tidb-cloud/*.md	Metric labels and Japanese descriptions now use consistent RU terminology.
TiFlash platform bullet restructuring tidb-resource-control-ru-groups.md	The TiDB Cloud platform block now includes both TiFlash flow-control and scheduling bullets.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🔵 Low · up to 79b09

The terminology updates are low risk, but TiDB Cloud readers may still be sent to an insecure, English self-managed documentation link instead of the applicable Japanese Cloud page. Correct the link before merge.

Suggested reviewers: invalid-email-address, qiancai

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly summarizes the main change: unifying Japanese Request Unit (RU) terminology.
Description check	✅ Passed	The description explains the terminology changes, affected files, target version, and AI involvement. The optional first-time contributor checklist is omitted, and the related-link fields are blank, b…

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (7 skipped: 7 unsupported.)

Full details: Description check

Explanation

The description explains the terminology changes, affected files, target version, and AI involvement. The optional first-time contributor checklist is omitted, and the related-link fields are blank, but the required information is otherwise complete.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests

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Actionable comments posted: 1

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ℹ️ Review info

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Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

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📥 Commits

Reviewing files that changed from the base of the PR and between 0cc9783 and 99cefe7.

📒 Files selected for processing (7)

• dashboard/dashboard-resource-manager.md
• grafana-resource-control-dashboard.md
• releases/release-6.6.0.md
• tidb-cloud/architecture-concepts.md
• tidb-cloud/manage-serverless-spend-limit.md
• tidb-cloud/select-cluster-tier.md
• tidb-resource-control-ru-groups.md

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Actionable comments posted: 1

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Team

Run ID: b28373bc-068a-4d41-afe3-af0c19f56901

📥 Commits

Reviewing files that changed from the base of the PR and between a82e814 and 79b0953.

📒 Files selected for processing (7)

• dashboard/dashboard-resource-manager.md
• grafana-resource-control-dashboard.md
• releases/release-6.6.0.md
• tidb-cloud/architecture-concepts.md
• tidb-cloud/manage-serverless-spend-limit.md
• tidb-cloud/select-cluster-tier.md
• tidb-resource-control-ru-groups.md

Included review availability: Your plan provides up to 4 included reviews per hour; 0 remain after this review.