tidb-lightning: recommend matching TiDB Lightning and TiDB versions (#23909)

[ti-chi-bot]

This is an automated cherry-pick of #23909

What is changed, added, or deleted? (Required)

Recommend using the same version of TiDB Lightning as the target TiDB cluster consistently across the deployment guide, FAQ, quick start, and troubleshooting documentation.

• Replace the blanket backward-compatibility claim and latest-version recommendation in the deployment guide with the matching-version recommendation.
• Reframe the FAQ as "Which TiDB Lightning version should I use?" and focus the answer on matching the target TiDB cluster version instead of historical minimum-version information.
• Specify the matching version in TiUP installation and quick-start launch examples, and retain the original task's version in the FAQ restart example.
• Align upgrade advice in both troubleshooting pages with the same recommendation.
• Address review feedback: use the documentation version variable in examples, link the installation step, clarify restart wording, and pin the Lightning version in the additional example-data and migration guides identified in review and their available translations.

This is a documentation guidance correction, not a product behavior change.

Validation: git diff --check and the repository's ./scripts/markdownlint passed for all changed Markdown files. The version-selection FAQ heading was changed; searches in both repositories found no references to its old anchor. The new Step 3 links were checked against the installation headings. No page aliases were changed. TiUP installation and version-pinned execution were also smoke-tested with Lightning v8.5.0; no data import was performed.

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

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)

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

• Related code change PR links (if applicable): N/A (documentation-only correction).
• This PR is translated from: N/A.
• Other reference link(s):
  • Chinese documentation PR: tidb-lightning: recommend matching TiDB Lightning and TiDB versions docs-cn#21945
  • https://docs.pingcap.com/zh/tidb/dev/deploy-tidb-lightning/
  • https://docs.pingcap.com/zh/tidb/dev/tidb-lightning-faq/

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 TiDB Lightning installation, startup, import, restart, and troubleshooting guidance to use an explicitly specified version.
  • Recommended matching the TiDB Lightning version with the target TiDB cluster version.
  • Clarified version selection in tutorials, deployment instructions, FAQs, and performance troubleshooting guidance.
  • Removed outdated guidance referencing unsupported early TiDB versions and generic “latest version” recommendations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository: pingcap/docs/.coderabbit.yaml

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 1b87c61e-4eca-4b38-9338-1c24d7c3e233

📥 Commits

Reviewing files that changed from the base of the PR and between 63ffe3e and 56e1919.

📒 Files selected for processing (8)

• get-started-with-tidb-lightning.md
• import-example-data.md
• migrate-from-sql-files-to-tidb.md
• migrate-large-mysql-to-tidb.md
• tidb-lightning/deploy-tidb-lightning.md
• tidb-lightning/tidb-lightning-faq.md
• tidb-lightning/troubleshoot-tidb-lightning.md
• tidb-troubleshooting-map.md

Included review availability: Your plan provides up to 4 included reviews per hour; 2 remain after this review.

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📝 Walkthrough

Walkthrough

The documentation replaces unversioned or latest-version TiDB Lightning commands with explicit versions that match the target TiDB cluster. Deployment, restart, FAQ, and troubleshooting guidance now uses the same version-matching rule.

Changes

TiDB Lightning version guidance

Layer / File(s)	Summary
Versioned installation and import commands get-started-with-tidb-lightning.md, import-example-data.md, migrate-from-sql-files-to-tidb.md, migrate-large-mysql-to-tidb.md, tidb-lightning/deploy-tidb-lightning.md	Installation, startup, and import commands now use tiup tidb-lightning:<version>. The instructions tell readers to match the version to the target TiDB cluster.
Deployment and restart guidance tidb-lightning/deploy-tidb-lightning.md, tidb-lightning/tidb-lightning-faq.md	Manual deployment and restart instructions now use the target cluster version. The FAQ replaces backend-version requirements with version-selection guidance.
Troubleshooting version guidance tidb-lightning/troubleshoot-tidb-lightning.md, tidb-troubleshooting-map.md	Troubleshooting guidance now recommends a newer TiDB Lightning release that matches the target TiDB cluster when upgrading.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Other

Suggested reviewers: qiancai

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main documentation change: recommending matching TiDB Lightning and TiDB cluster versions.
Description check	✅ Passed	The description is complete and follows the required template. It explains the changes, affected version, related links, AI involvement, validation, and applicable change classifications.
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

🧪 Generate unit tests (beta)

• Create a new PR

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[qiancai]

/approve

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