* fix(validate-sidebar): replace subdirectory heuristic with locale pattern matching
detectLanguageDirs() previously classified any top-level docs/ directory
containing subdirectories as a translation language. This was too broad —
if an English section ever gained nested subfolders it would be silently
excluded from validation.
Replaced with a BCP 47 locale-code regex (/^[a-z]{2}(?:-[a-zA-Z]{2})?$/)
that matches known patterns (cs, fr, vi-vn, zh-cn) and won't falsely
classify content sections like explanation/ or reference/.
* fix(validate-sidebar): guard drift check against undefined order values
extractSidebarOrder() returns { hasSidebar: false } when no sidebar block
exists, leaving order as undefined rather than null. The drift check only
guarded against null, allowing undefined values to emit noisy warnings
like "Order drift: ... order undefined".
Changed the guard to typeof === 'number' which correctly excludes both
undefined and null without relying on a specific sentinel value.
* chore(validate-sidebar): add JSDoc docstrings to all functions
Adds @param and @returns annotations to extractSidebarOrder,
detectLanguageDirs, getEnglishSections, checkDirectory,
checkTranslationDrift, and relativePath.
Adds tools/validate-sidebar-order.js to validate sidebar.order values
in YAML frontmatter across English and translated docs.
Checks for duplicate orders, gaps in sequence, and missing order fields.
For translations, also warns on order drift from English counterparts.
Wired into the quality script as docs:validate-sidebar.
Emmanuel Atsé