feat: migrate website-creator from Next.js+Payload to Astro+Tina CMS

Major changes:
- Replace Payload CMS with Tina CMS (self-hosted)
- Add Astro DB for consent logging (PDPA compliant)
- Update Tailwind v3 to v4 (@tailwindcss/vite plugin)
- Add astro-tina-starter template
- Rewrite consent template for Astro (ConsentBanner.astro, Astro DB, Nano Stores)
- Add install-tina-backend.sh for self-hosted Tina per customer
- Rename convert-astro.sh to migrate-tina.sh
- Add AGENTS.md template for generated websites
- Delete all Payload/Next.js files

Technical updates:
- Astro DB using defineDb with eq operators for queries
- Tailwind v4 with @theme block
- Tina CMS local development mode
- Proper Astro API routes for consent

Research-verified with official documentation (April 2026)

skills/website-creator/templates/astro-tina-starter/.tina/schema.ts

@@ -0,0 +1,91 @@
+import { defineSchema } from 'tinacms'
+
+export const schema = defineSchema({
+  collections: [
+    {
+      name: 'post',
+      label: 'Posts',
+      path: 'src/content/posts',
+      format: 'mdx',
+      fields: [
+        {
+          type: 'string',
+          name: 'title',
+          label: 'Title',
+          required: true,
+        },
+        {
+          type: 'string',
+          name: 'description',
+          label: 'Description',
+        },
+        {
+          type: 'datetime',
+          name: 'publishedAt',
+          label: 'Published At',
+        },
+        {
+          type: 'string',
+          name: 'category',
+          label: 'Category',
+          options: ['news', 'blog', 'tutorial'],
+        },
+        {
+          type: 'rich-text',
+          name: 'body',
+          label: 'Body',
+          isBody: true,
+        },
+      ],
+    },
+    {
+      name: 'page',
+      label: 'Pages',
+      path: 'src/content/pages',
+      format: 'mdx',
+      fields: [
+        {
+          type: 'string',
+          name: 'title',
+          label: 'Title',
+          required: true,
+        },
+        {
+          type: 'string',
+          name: 'description',
+          label: 'Description',
+        },
+        {
+          type: 'rich-text',
+          name: 'body',
+          label: 'Body',
+          isBody: true,
+        },
+      ],
+    },
+    {
+      name: 'settings',
+      label: 'Settings',
+      path: 'src/content/settings',
+      format: 'json',
+      fields: [
+        {
+          type: 'string',
+          name: 'siteName',
+          label: 'Site Name',
+        },
+        {
+          type: 'string',
+          name: 'siteDescription',
+          label: 'Site Description',
+        },
+        {
+          type: 'string',
+          name: 'language',
+          label: 'Language',
+          options: ['th', 'en', 'th-en'],
+        },
+      ],
+    },
+  ],
+})