[ety001]

T7-3: Localize steem-js core tutorials for all 7 locales

Adds the tutorials-chapter steem-js trio — index (Getting Started), read-api (Reading Chain Data), broadcast (Broadcasting Operations) — translated into zh, ru, fr, de, it, es, ko: 21 new pages.

What's in this PR

• 21 pages: docs/<lc>/tutorials/steem-js/{index,read-api,broadcast}.md for lc ∈ {zh, ru, fr, de, it, es, ko}.
• config.mts: one new Tutorials sidebar group per locale, inserted between Guides and Services (zh=教程, ru=Обучающие материалы, fr=Tutoriels, de=Tutorials, it=Tutorial, es=Tutoriales, ko=튜토리얼), each carrying exactly the three steem-js items. Root/en untouched.

Guarantees

• Code fences byte-identical to en: every page keeps the exact fence count of its en source (index: 21 blocks, read-api: 118, broadcast: 31) and every fenced line — including JS comments — is copied byte-for-byte. Verified by an independent reconciliation script over all 21 pages (PASS).
• Terminology: each page follows the frozen <lc>-glossary.json baseline (first occurrence annotated 译法/표기 (English)); steem-js/@steemit/steem-js/JSON-RPC/STEEM/SBD/VESTS/condenser_api etc. left untranslated; method/parameter/field/config-key names kept in English.
• En defects preserved as-is, e.g. the prematurely closed fence at index.md L254–255 in the Multiple API Instances section (stray }); outside the fence) — worth a follow-up fix in en upstream.
• Explicit # headings are preserved in English per task spec (frontmatter title/description are translated).
• En pages under docs/tutorials/ are untouched (git diff clean).

Link policy note

Links to the two sibling steem-js pages not yet localized on this branch (signed-calls.html) intentionally keep the en path (/tutorials/steem-js/signed-calls.html) instead of the locale prefix — VitePress fails the build on dead links, and the locale counterparts are landing in parallel PRs. Same pattern already used by docs/zh/api/index.md for not-yet-localized targets. Links to the three pages added here use /<lc>/tutorials/...; /api/ links use /<lc>/api/... (locale method pages are generated at build time by pnpm docs:gen).

Verification

• Fence reconciliation script: all 21 pages PASS (counts + byte-identical fenced content).
• All 21 frontmatters parse as valid YAML.
• NODE_OPTIONS=--max-old-space-size=8192 pnpm build → exit 0 (build complete in ~308s; dist contains docs/<lc>/tutorials/steem-js/*.html for all locales).