Add French and Korean Seed Documentation

What does this MR do and why?

Establishes the doc-locale/fr-fr/ and doc-locale/ko-kr/ folder structure in the GitLab project and contributes the first round of seed content generated with CI Translation Components from this MR, along with all supporting CI, linting, and ownership infrastructure.

Changes included:

• Adds @gitlab-com/localization/maintainers/french and @gitlab-com/localization/maintainers/korean as CODEOWNERS of the new doc-locale/fr-fr/ and doc-locale/ko-kr/ directories.
• Adds seed translations for doc-locale/fr-fr/user/duo_agent_platform/_index.md (French) and doc-locale/ko-kr/user/duo_agent_platform/_index.md (Korean), produced via CI Translation Components. These will be updated as human-reviewed versions arrive from the Argo ↔️ Phrase workflow.
• Updates the docs-i18n-lint links lychee job to exclude (ja-jp|ko-kr|fr-fr)/developer paths (previously only excluded ja-jp/development.*#).
• Adds .docs-ko-kr-patterns and .docs-fr-fr-patterns file-change anchors and corresponding .docs:rules:docs-i18n-lint-korean and .docs:rules:docs-i18n-lint-french rule sets in rules.gitlab-ci.yml.
• Adds docs-i18n-lint korean-vale and docs-i18n-lint french-vale CI jobs in docs.gitlab-ci.yml, reusing the existing i18n_lint_language_vale.sh script with LANGUAGE_CODE / LANGUAGE_NAME variables.
• Adds Vale configuration (.vale.ini, output template vale.tmpl, and empty locale_rules/ directory) for both doc-locale/ko-kr/ and doc-locale/fr-fr/.
• Adds route mappings for ko-kr and fr-fr in .gitlab/route-map.yml to enable "View on docs site" links in merge requests.
• Updates doc/development/documentation/testing/_index.md with Korean and French language support sections, documenting the new Vale linting jobs and their trigger conditions.
• Adds Danger spec coverage for Korean and French localized doc changes in spec/tooling/danger/documentation_spec.rb.
• Fixes a trailing whitespace in .gitlab/duo/mr-review-instructions.yaml.

Related issues

• Closes gitlab-com/localization/docs-site-localization#879 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Pull branch down
2. Run each CI job command locally

MR acceptance checklist

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