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/lib/AGENTS.md

@@ -2,11 +2,11 @@
 
 ## Purpose
 
-跨層基礎工具：環境變數、DB 連線、後台認證、表單驗證、AI 生成、Markdown 處理、媒體 URL／R2 清理。
+跨層基礎工具：環境變數、DB 連線、後台認證、表單驗證、AI 生成、Markdown 處理、媒體 URL／R2 清理、schema.org JSON-LD。
 
 ## Ownership
 
-- 擁有 `src/lib/` 七個檔案：`env.ts`、`db.ts`、`auth.ts`、`form.ts`、`ai.ts`、`markdown.ts`、`media.ts`。
+- 擁有 `src/lib/` 八個檔案：`env.ts`、`db.ts`、`auth.ts`、`form.ts`、`ai.ts`、`markdown.ts`、`media.ts`、`schema-org.ts`。
 - 其他層（pages / data / middleware）只消費，唔好複製呢度嘅邏輯。
 
 ## Local Contracts
@@ -27,6 +27,7 @@
   - `generateBlogPost(db, env, input)` 同步生成：`{ mode: "topic" }` 或 `{ mode: "next" }`（攞佇列下一個 pending）；一律存 **draft** 並將關鍵字標記 `generated`。缺 `AI_API_KEY` / 未啟用時回 `{ ok: false, error }`，唔會 throw。
 - **`markdown.ts`**：`renderMarkdown`（`marked`，內容受信任所以**唔 sanitize**）、`slugify`（保留中文）、`autoExcerpt`。
 - **`media.ts`**：媒體 URL 同 R2 清理。`MEDIA_PREFIX = "/media/"`、`mediaUrl(key)` 砌對外 URL、`mediaKey(url)` 由 `/media/...` 取 R2 key（唔係前綴回 `null`）、`deleteMedia(env, url)` 刪除對應 R2 物件（外部 URL／空值唔理，失敗唔 throw）。
+- **`schema-org.ts`**：schema.org JSON-LD 建構器，只砌資料、唔負責輸出（輸出喺 `Base.astro` 嘅 `jsonLd` prop）。匯出 `localBusiness(settings, origin)`、`faqPage(items)`（無題目回 `null`）、`blogPosting(post, settings, origin)`、`breadcrumbs(origin, trail)`。所有欄位 optional，冇資料就唔加，避免空值 schema。
 
 ## Work Guidance
 

src/lib/schema-org.ts

@@ -0,0 +1,79 @@
+import type { Settings } from "../data/content";
+import type { ContentItem, Post } from "../db/schema";
+
+/**
+ * schema.org (JSON-LD) 建構器。
+ * 只負責砌資料，唔負責輸出；輸出喺 Base.astro 嘅 jsonLd prop。
+ * 所有欄位都係 optional，冇資料就唔加，避免出現空值 schema。
+ */
+
+function withContext<T extends Record<string, unknown>>(obj: T): T & { "@context": string } {
+  return { "@context": "https://schema.org", ...obj };
+}
+
+function companyName(settings: Settings): string {
+  return settings.company_name || settings.company_short_name || "盈豐太陽能工程有限公司";
+}
+
+/** 本地商戶（首頁）。 */
+export function localBusiness(settings: Settings, origin: string) {
+  const sameAs = settings.facebook_url ? [settings.facebook_url] : undefined;
+  return withContext({
+    "@type": "LocalBusiness",
+    "@id": `${origin}/#business`,
+    name: companyName(settings),
+    url: `${origin}/`,
+    ...(settings.seo_default_description ? { description: settings.seo_default_description } : {}),
+    ...(settings.phone ? { telephone: settings.phone } : {}),
+    ...(settings.email ? { email: settings.email } : {}),
+    ...(settings.address
+      ? { address: { "@type": "PostalAddress", streetAddress: settings.address, addressCountry: "HK" } }
+      : {}),
+    ...(settings.og_image ? { image: settings.og_image } : {}),
+    ...(sameAs ? { sameAs } : {}),
+  });
+}
+
+/** 常見問題（首頁 FAQ）。冇問題就唔輸出。 */
+export function faqPage(items: ContentItem[]) {
+  if (items.length === 0) return null;
+  return withContext({
+    "@type": "FAQPage",
+    mainEntity: items.map((item) => ({
+      "@type": "Question",
+      name: item.title,
+      acceptedAnswer: { "@type": "Answer", text: item.description },
+    })),
+  });
+}
+
+/** Blog 文章。 */
+export function blogPosting(post: Post, settings: Settings, origin: string) {
+  const publisher = companyName(settings);
+  const url = `${origin}/blog/${post.slug}`;
+  return withContext({
+    "@type": "BlogPosting",
+    headline: post.title,
+    url,
+    mainEntityOfPage: url,
+    ...(post.metaDescription || post.excerpt ? { description: post.metaDescription || post.excerpt } : {}),
+    ...(post.publishedAt ? { datePublished: post.publishedAt.toISOString() } : {}),
+    dateModified: (post.updatedAt ?? post.publishedAt ?? new Date()).toISOString(),
+    ...(post.coverImage ? { image: post.coverImage } : {}),
+    author: { "@type": "Organization", name: publisher },
+    publisher: { "@type": "Organization", name: publisher },
+  });
+}
+
+/** 麵包屑。trail 由外至內，path 以 "/" 開頭。 */
+export function breadcrumbs(origin: string, trail: { name: string; path: string }[]) {
+  return withContext({
+    "@type": "BreadcrumbList",
+    itemListElement: trail.map((item, i) => ({
+      "@type": "ListItem",
+      position: i + 1,
+      name: item.name,
+      item: `${origin}${item.path}`,
+    })),
+  });
+}