fix(i18n-ja): correct unnatural Japanese translations in multiple files

[yahonda]

What is changed and how it works?

This PR fixes unnatural Japanese translations introduced by the machine translation commit 1e2e78a on the `i18n-ja-release-8.5` branch.

Major corrections

• Fixed critical mistranslations (e.g., 閲覧数 -> ビュー, 発現インデックス -> 式インデックス, 取引 -> トランザクション, 悲観的な取引 -> 悲観的トランザクション, 1個 -> 1PC)
• Corrected duplicate product names (e.g., TiDB TiDB Lightning -> TiDB Lightning, TiDB TiDB Cloud -> TiDB Cloud)
• Fixed incorrect katakana transliterations (e.g., ティクヴ -> TiKV, 配置Driver -> Placement Driver)
• Corrected garbled sentence structures (e.g., progress grep word order, "last line in log" -> "last line of log")
• Replaced inappropriate upstream/downstream terminology with proper Japanese database terminology (上流/ターゲット)
• Fixed other typos and formatting issues across 29 files

Check List

• Manual test (add detailed scripts or steps below)
• No code
• TiDB Cloud / TiDB documentation
• English / Japanese documentation
• No need for documentation update (this is a translation fix)

Release note

• None

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[gemini-code-assist]

Code Review

This pull request improves the Japanese documentation for TiDB and TiDB Cloud by correcting translation errors, fixing typos (such as correcting "ティクヴ" to "TiKV" and "行く" to "Go"), and refining Japanese phrasing for better readability. The review feedback is highly constructive and focuses on further polishing the text. It identifies remaining terminology inconsistencies (such as standardizing "storage容量" to "ストレージ容量" and "クラスタ" to "クラスター"), points out minor grammatical issues, and suggests removing unnecessary half-width spaces between English and Japanese characters to ensure a consistent and professional style across all documents.

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