docs: add S3 Tables and PyIceberg guides in five languages

[GatewayJ]

Summary

Document the built-in RustFS S3 Tables catalog and a PyIceberg create, append, reload, and scan walkthrough in English, Chinese, German, French, and Japanese. Add sidebar entries and links from administration and the existing external-catalog integration guide.

The guides cover preview status, SigV4 and path-style configuration, permissions, identifier constraints, Iceberg v1/v2 support, custom table locations, and catalog-only deletion with its maintenance limits. Implementation claims are checked against RustFS commit 7e0c6711.

Validation

• npm run docs:check — passed, including navigation, links, locale page parity, and translated code blocks.
• ALGOLIA_ADMIN_API_KEY= npm run build — passed; search-index upload disabled.
• git diff --check and git diff --cached --check — passed.
• Locale audit for zh,de,fr,ja — no errors on the ten new pages; four warnings retain the S3 Tables product title. Code blocks and inline technical tokens match across all five languages.
• Browser preview — verified the Chinese tutorial, cleanup notice before the commands, links, and switching to the corresponding English page.

Known limitations

• npm run types:check reports 13 existing implicit-any errors in scripts/add-language-redirects.mjs and worker.mjs, also reproduced on the unchanged base commit.
• The client examples were checked against upstream source; a live RustFS/PyIceberg end-to-end run was not completed.
• Existing untranslated content elsewhere in the repository is outside this change.

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