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/astro.config.mjs

@@ -0,0 +1,37 @@
+import { defineConfig } from 'astro/config'
+import tailwindcss from '@tailwindcss/vite'
+import tina from 'tinacms'
+import { fileURLToPath } from 'url'
+import path from 'path'
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
+
+export default defineConfig({
+  integrations: [
+    tina({
+      enabled: !!process.env.TINA_TOKEN,
+      sidebar: {
+        partials: [],
+      },
+    }),
+  ],
+  vite: {
+    plugins: [tailwindcss()],
+    resolve: {
+      alias: {
+        '@': path.resolve(__dirname, './src'),
+        '@components': path.resolve(__dirname, './src/components'),
+        '@layouts': path.resolve(__dirname, './src/layouts'),
+        '@styles': path.resolve(__dirname, './src/styles'),
+        '@content': path.resolve(__dirname, './src/content'),
+      },
+    },
+  },
+  output: 'static',
+  build: {
+    assets: '_assets',
+  },
+  server: {
+    port: 4321,
+  },
+})