i18n(ja): fix changefeed capacity heading, states mistranslation, and status/state term drift

[yahonda]

What is changed, added or deleted? (Required)

tidb-cloud/changefeed-overview.md:

• ## Query changefeed capacity was translated as a broken word-for-word transliteration (クエリ変更フィード容量, no particles), breaking from this document's own consistent heading pattern ([Object]を[Verb]する, e.g. 変更フィードを作成する). Reworded to 変更フィードの容量をクエリする.
• Within that same section, "query" was translated two different ways for the identical EN word: 照会 (inquire/check) in the intro sentence vs クエリを実行 (execute a query, the SQL-query sense) in step 2. Unified to the checking-a-value sense.
• "TiCDC Changefeed Capacity Units (CCUs)" left "Changefeed" untranslated in 3 places while the parallel dedicated-tier term correctly translates "Replication" (TiCDC レプリケーション容量ユニット). Unified to TiCDC 変更フィード容量ユニット, matching this document's own changefeed→変更フィード convention.
• "The states are described as follows" was mistranslated as 各州 (each US-style state/province) instead of 状態 (state/condition) — a false-friend error with no sensible meaning in a changefeed-state-machine context.

TOC files (TOC.md and the 4 tidb-cloud plan variants): two navigation labels used 状態 (state) while the linked page's own title uses ステータス (status, katakana) for the same English word — サーバー状態変数 vs status-variables.md's own サーバーステータス変数, and クラスタの状態を確認する vs post-installation-check.md's own クラスタのステータスを確認する. Unified the TOC labels to match each target page's own established term.

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

• master (the latest development version)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.2 (TiDB 8.2 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)

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

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

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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