add v7.5.8 release notes

[doc-claw-bot]

What is changed, added or deleted? (Required)

• Add releases/release-7.5.8.md for the TiDB 7.5.8 patch release notes.
• Add the TiDB 7.5.8 entry to TOC-tidb-releases.md, releases/_index.md, and releases/release-timeline.md.
• Fill in the TiDB 7.5.8 release date.
• This release-notes update is prepared on release-8.5 because the release-notes directory is maintained there and will be cherry-picked to master.

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

• master (the latest development version)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.2 (TiDB 8.2 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)?

• This PR is translated from: add v7.5.8 release notes docs#23757
• Other reference link(s): generated from doc_4afdcdb19e49_release-7.5.8-updated-by-ai.md

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

[coderabbitai]

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📝 Walkthrough

Walkthrough

新增 TiDB 7.5.8 发布说明文档。文档包含版本信息、部署链接、PD 监控指标改进，以及 TiDB、TiKV、PD、TiFlash 和 TiCDC 的错误修复条目。

Changes

TiDB 7.5.8 发布说明

Layer / File(s)	Summary
发布说明基础信息 releases/release-7.5.8.md	新增 front matter、版本信息、发布日期占位，以及试用、生产部署和离线包下载链接。
监控改进与 TiDB 修复 releases/release-7.5.8.md	记录 pd_cluster_status 新增 store 标签，以及 TiDB 中 UNION 查询崩溃、规划期 CPU 消耗过高和异步加载统计信息 panic 的修复。
组件错误修复 releases/release-7.5.8.md	记录 TiKV、PD、TiFlash 和 TiCDC 的错误修复，包括 panic、GC safepoint、内存配额、数据一致性和 Kafka client 泄漏问题。

Priority: ⬇️ Low

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

Change: Other

Merge Risk: ⚪ Minimal · up to 99ba8

This change adds release notes only, with no identified merge-blocking risk.

🚥 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	标题“add v7.5.8 release notes”简洁明确，准确概括了新增 TiDB 7.5.8 发布说明这一主要变更。
Description check	✅ Passed	描述包含变更内容、适用版本、相关链接、AI 参与情况和变更类型检查项。内容与 PR 目标一致，满足必填信息要求。

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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Actionable comments posted: 1

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[YuJuncen]

rest LGTM for BR

[YuhaoZhang00]

the rest LGTM for PD

[ti-chi-bot]

@YuhaoZhang00: adding LGTM is restricted to approvers and reviewers in OWNERS files.

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In response to this:

the rest LGTM for PD

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[ti-chi-bot]

@JaySon-Huang: adding LGTM is restricted to approvers and reviewers in OWNERS files.

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-09-17 03:51:19.776630102 +0000 UTC m=+263525.714287716: ☑️ agreed by overvenus.
• 2026-09-17 06:40:29.678801893 +0000 UTC m=+273675.616459477: ☑️ agreed by qiancai.

[qiancai]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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Needs approval from an approver in each of these files:

• OWNERS [qiancai]

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch master: #21939.