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/pages/blog/index.astro

@@ -26,5 +26,5 @@ Astro.response.headers.set("Cache-Control", "public, s-maxage=60, stale-while-re
   description={settings.seo_default_description || "村屋太陽能嘅實用資訊、安裝心得同回本分析。"}
   image={settings.og_image}
 >
-  <BlogIndex posts={items} settings={settings} client:load />
+  <BlogIndex posts={items} settings={settings} client:idle />
 </Base>