Move seed.sql out of migrations and add SEO structured data

- Relocate seed.sql to scripts/ so wrangler d1 migrations apply
  doesn't treat it as a migration; update package.json, setup.mjs,
  README, and all AGENTS.md references.
- Add src/lib/schema-org.ts builders (LocalBusiness, FAQPage,
  BlogPosting, BreadcrumbList) and emit JSON-LD via Base.astro.
- Add lastmod to sitemap entries.
- Set real site domain, worker route, and D1/KV ids.
- Improve image loading hints and heading semantics across site
  components; switch BlogIndex to client:idle.

src/components/site/Cases.tsx

@@ -30,6 +30,8 @@ export function Cases({ items }: { items: CaseStudy[] }) {
               w="full"
               aspectRatio={{ base: "4 / 3", lg: "16 / 10" }}
               objectFit="cover"
+              loading="lazy"
+              decoding="async"
               transition="transform .5s"
               _groupHover={{ transform: "scale(1.03)" }}
             />
@@ -66,6 +68,8 @@ export function Cases({ items }: { items: CaseStudy[] }) {
                     w="full"
                     aspectRatio="4 / 3"
                     objectFit="cover"
+                    loading="lazy"
+                    decoding="async"
                     transition="transform .5s"
                     _groupHover={{ transform: "scale(1.03)" }}
                   />