docs: improve HTAP and Index terminology for better localization

[yahonda]

This PR improves technical terminology in the English source to ensure more natural and accurate machine translations in other languages (specifically Japanese).

Changes:

1. Changed 'storage links' to 'data pipelines' in the HTAP context.
2. Changed 'storage model' to 'storage format' in the Secondary Indexes context.
3. Changed 'region re-election' to 'region leader re-election' in the log backup architecture context to accurately reflect the Raft protocol where leaders, not regions, are elected.

These updates use more standard technical English, which helps translation engines produce clearer localized versions without the need for manual post-editing of awkward direct translations.

[ti-chi-bot]

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[gemini-code-assist]

Code Review

This pull request updates the TiDB best practices documentation by changing "reduce storage links" to "reduce data pipelines" for clarity. The reviewer suggested a further improvement to use a more direct, active tone ("You want" instead of "You hope to have") and to simplify the phrasing to "simplified data pipelines", which aligns with the repository's style guide to avoid unnecessary words.

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-05-26 07:24:59.796040876 +0000 UTC m=+336969.766205938: ☑️ agreed by qiancai.