i18n(ja): fix だ/である plain-style sentences stranded in polite prose

[yahonda]

What is changed, added or deleted? (Required)

Corpus-wide scan for です/ます (polite) vs だ/である (plain/literary) sentence-register mixing: files that are overwhelmingly polite but have a stray plain-style sentence or paragraph, which reads jarring against the surrounding voice. Each site verified against EN and fixed to match the file's dominant polite register (9 files):

• releases/release-6.5.0.md: not just a register issue - the clause was also word-order scrambled and missing ます entirely, garbling which statement types are supported. Rewritten to match EN.
• develop/java-app-best-practices.md, develop/dev-guide-connection-parameters.md, information-schema/information-schema-inspection-result.md, optimistic-transaction.md, grafana-pd-dashboard.md: one stray plain-ending sentence each, mismatching immediate sibling sentences/bullets.
• tidb-lightning/tidb-lightning-physical-import-mode-usage.md: two plain sentences in the same line fixed together.
• dr-secondary-cluster.md: a whole 4-sentence paragraph was plain-style, sandwiched between polite text - fixed all 4 sentences together.
• pessimistic-transaction.md: a 3-sentence plain paragraph plus one bullet mismatching its sibling above.

This is the first batch from an ongoing scan; more candidates (bullet-list/table-cell style, which need per-list context judgment) are still being verified and may follow as additional commits on this PR.

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

• i18n-ja-release-8.5 (TiDB Japanese documentation for TiDB 8.5 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):

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

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