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.

.astro/dev.json

@@ -1,14 +1,14 @@
 {
-	"pid": 98774,
-	"port": 4321,
-	"url": "http://localhost:4321",
+	"pid": 52048,
+	"port": 4322,
+	"url": "http://localhost:4322",
 	"urls": {
 		"local": [
-			"http://localhost:4321/"
+			"http://localhost:4322/"
 		],
 		"network": [],
 		"networkInterfaceNames": []
 	},
-	"background": true,
-	"startedAt": "2026-09-11T08:49:14.193Z"
+	"background": false,
+	"startedAt": "2026-09-13T08:12:40.425Z"
 }