feat(07-03): enrich blog listing with D-16 useSeoMeta + CollectionPage/Breadcrumb JSON-LD
- Add SITE_URL + OG_FALLBACK constants (fallback hardcoded, resolveOgImage helper owned by 07-02)
- Extend useSeoMeta: ogImage (absolute /og-blog-default.jpg), ogUrl, ogLocale, ogLocaleAlternate, twitterCard, twitterImage
- Add useSchemaOrg([defineWebPage CollectionPage, defineBreadcrumb(Accueil -> Blog)])
- inLanguage resolved at setup (type constraint: literal union, not ComputedRef)
- Requirements: SEO-10, SEO-13, SEO-15
kayjaydee
d2ab5681da