v0.29.0 — Multi-language support (i18n foundation)

Makes Refrakt's framework-generated text — labels, navigation chrome, accessibility strings, structural headings, and client-side behavior strings — localizable, so a site built for a non-English locale no longer shows English UI chrome around translated content. This milestone delivers the string-resolution foundation of SPEC-035. Serving the same site in multiple languages (route trees, switcher, auto-detect) remains a deliberate Non-Goal that this foundation is explicitly constrained to allow later without breaking changes.