Linq channel code was fully integrated but missing from documentation
surfaces. Add Linq to architecture tables, channels reference, and
config reference so users can discover and configure the channel.
Use correct ISO 639-1 language code (vi) instead of country code (vn),
consistent with existing translations (zh-CN, ja, ru).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
