i18n(ja): restore DM-master and DM-worker as literal English terms

[yahonda]

What is changed, added or deleted? (Required)

DM-master and DM-worker are the actual TiDB Data Migration (DM) tool component/binary names (matching the dm-master/dm-worker binaries and dm/master, dm/worker paths), not descriptive nouns that should be translated. This corpus rendered them inconsistently as katakana DMマスター/DMワーカー in many places while other places already correctly kept them literal (DM-master/DM-worker).

This PR unifies all katakana occurrences to the literal English form, matching the direction already decided in a prior term-notation review.

• DMマスター → DM-master
• DMワーカー → DM-worker

56 files, 265 sites. Heading anchors ({#...}) were already stable English slugs, independent of the visible heading text, so none needed changing.

Generic uses of bare マスター/ワーカー (e.g. "master branch", other components) are unrelated to this term and were not touched — only the DM-prefixed forms were in scope.

Verified markdownlint-cli2 clean on all touched files.

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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