docs: fix specific repeated component names in Japanese

[yahonda]

Fixed repeated words in Japanese documentation:

• TiDB TiDB Cloud -> TiDB Cloud
• TiDB TiDB Cloud Starter -> TiDB Cloud Starter
• TiFlashTiFlash -> TiFlash

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[gemini-code-assist]

Code Review

This pull request corrects redundant product name prefixes and typos across multiple Japanese documentation files, including the TiDB Cloud introduction and resource control guides. The review feedback identifies several opportunities to improve grammatical correctness, such as fixing incomplete sentences and missing particles, and ensures terminology consistency by standardizing the spelling of technical terms like 'cluster' and removing unnecessary spaces.