Restructure localization docs, document XLIFF extract/compose workflow

[martyanovandrey]

Problem

The Localization page (tools/docs/translate.md) mixed an overview, the Yandex Translate provider reference and file filtering into one article. The extract and compose subcommands were barely mentioned: a single intro sentence plus an orphan table with one option. The page also contained two dangling anchors - #cat and #json-schemas pointed to sections that do not exist.

Changes

The section is now a hub with three child articles (both locales, ru + en):

• Localization (translate.md, URL preserved) - overview of the three translation methods, how the translation pipeline works (segmentation, markup protection), what gets translated (md + yaml/json via schemas, closes the dangling #json-schemas anchor), common parameters, list-file filtering and no-translate content markers.
• Machine translation (translate-yandex.md, new) - the default Yandex Translate provider: auth token types, folder, glossary, limits and TRANSLATE_LIMIT_EXCEED.
• AI translation (translate-ai.md) - untouched except cross-links updated to the new structure.
• XLIFF exchange with CAT tools (translate-xliff.md, new) - the extract/compose round trip: xliff + skl pair mechanics, full cycle example, XLIFF 1.2 format with inline <g>/<x/> tags, and full parameter reference for both subcommands (--filter, --schema, --no-ref-resolve, --use-source).

All parameter descriptions verified against @diplodoc/cli v5.55 sources. Existing anchors (#auto, #file-filter, #content-filter) are kept on the hub page, and the previously broken dash characters in the no-translate examples are fixed.

Both locales build cleanly with yfm build v5.57 (no new lint warnings).

[github-actions]

✅ Documentation build

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Build logs

Warnings (2)

⚠️ en/guides/openapi.md: 168: YFM001 / inline-code-length Inline code length [Expected: 100; Actual: 265] [Context: " — the specification is displayed directly on the page (default value). If the size of the specification's json schema exceeds the value of ##maxOpenapiIncludeSize## (100 KB by default), the mode automatically switches to "]

⚠️ en/tools/docs/build.md: 50: YFM001 / inline-code-length Inline code length [Expected: 100; Actual: 109] [Context: " — a snapshot of the dependency graph (pages, included files, assets, missing paths, edge count), as well as "]