[vitormattos]

Summary

Make LibreSign's Translation developer-manual page the canonical place for contributor guidance on source-string translations and TRANSLATORS hints.

The LibreSign application PR #9364 previously added this detailed guidance to CONTRIBUTING.md. This PR keeps the durable documentation in the documentation repository; #9364 will retain only a short link to this page and its existing automated lint safeguard.

Changes

• Extend the existing developer_manual/translation.rst page, retaining its Transifex instructions.
• Explain the LibreSign style convention (TRANSLATORS without a colon), where hints belong, when separate hints are needed, and why same-line conditional translations are ambiguous to the Nextcloud extractor.
• Include concrete TypeScript and Vue examples and the exact lint and checker-test commands.
• Link Translation from the developer manual's start page.

No translation catalog, generated Sphinx HTML, or screenshot images are committed to the repository.

Rendered documentation

Screenshots captured with Chromium/Playwright from the actual Sphinx-generated HTML of this branch:

Full Translation page — rendered output

Validation

• sphinx-build -W developer_manual _build/developer_manual — passed, no warnings.
• Verified the rendered Translation page contains the new section, source examples, and lint commands.
• Captured and visually inspected the real rendered page; browser had no page errors.
• git diff --check — passed.

Cross-repository coordination: Review alongside LibreSign/libresign#9364, which will replace the duplicated CONTRIBUTING.md tutorial with a link to this page. No merge is requested as part of this PR.