i18n(ja): Fix product and technical term mistranslations

[yahonda]

• Dumpling: 団子 -> Dumpling
• Raft Engine: いかだエンジン -> Raft Engine
• Raftstore: いかだストア -> Raftstore
• TiFlash: ティフラッシュ -> TiFlash
• Pump: ポンプ -> Pump
• Reparo: レパロ -> Reparo
• tiup: ティアップ -> tiup
• GitHub repo names: fix Japanese translations in credits.md

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[gemini-code-assist]

Code Review

This pull request corrects several machine-translated or incorrect technical terms in the Japanese documentation, restoring them to their standard English names (such as "TiUP Playground", "Reparo", "Dumpling", "Raft", and various repository names). The review feedback suggests further minor improvements for consistency and natural phrasing, specifically recommending the use of "TiDBセルフマネージド" instead of "TiDB 自己管理" in ai/quickstart-via-python.md and capitalizing "tiup" as "TiUP" in tiup/tiup-mirror.md.