i18n(ja): restore literal English error messages in DM precheck troubleshooting

[yahonda]

First-time contributors' checklist

What is changed, added or deleted? (Required)

Seven heading-level error messages in this troubleshooting doc are quoted-string literals in the EN source (actual DM/TiDB Cloud error text a user would see verbatim on screen), but were translated into Japanese prose instead of kept as literal English. This defeats the doc's purpose as a troubleshooting reference organized by "find the exact message you saw" — a reader can't match a Japanese paraphrase against the English text actually shown by the product.

The file's other, non-quoted "Error message: ..." headings are plain descriptive section labels (not literal on-screen text) and were correctly left translated — only the 7 quoted ones needed restoring.

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
  • Updated seven migration error section headings to display the original English error messages.
  • Preserved existing section links and explanatory content.
  • Refined wording in the TiDB cluster storage guidance.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Reviewing files that changed from the base of the PR and between 3425c1f and e9a0f9f.

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• tidb-cloud/tidb-cloud-dm-precheck-and-troubleshooting.md

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📝 Walkthrough

Walkthrough

Seven troubleshooting headings now use the original English error messages. Anchor IDs remain unchanged. One TiKV storage sentence also has a minor Japanese wording change.

Changes

DM troubleshooting documentation

Layer / File(s)	Summary
Update troubleshooting error headings tidb-cloud/tidb-cloud-dm-precheck-and-troubleshooting.md	Seven headings under “移行エラーとその解決策” now use the original English error messages. Their anchor IDs and section bodies remain unchanged, except for one TiKV storage sentence that changes “増やす” to “増やして”.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~3 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to e9a0f

This documentation update introduces no material merge risk.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: restoring literal English DM precheck error messages in the Japanese troubleshooting documentation.
Description check	✅ Passed	The description explains the change, scope, affected documentation version, AI involvement, and applicable change categories. It is sufficiently complete, although the first-time contributor checklist…
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.

✨ 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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[yahonda]

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