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/db/config.ts

@@ -0,0 +1,22 @@
+import { defineDb, defineTable, column } from 'astro:db';
+
+const ConsentLog = defineTable({
+  columns: {
+    id: column.number({ primaryKey: true }),
+    action: column.text(),
+    purpose: column.text(),
+    analytics: column.boolean({ default: false }),
+    marketing: column.boolean({ default: false }),
+    functional: column.boolean({ default: false }),
+    userAgent: column.text({ optional: true }),
+    ip: column.text({ optional: true }),
+    timestamp: column.date(),
+    sessionId: column.text({ optional: true }),
+  },
+});
+
+export default defineDb({
+  tables: {
+    ConsentLog,
+  },
+});