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/tsconfig.json

@@ -0,0 +1,17 @@
+{
+  "extends": "astro/tsconfigs/strict",
+  "compilerOptions": {
+    "baseUrl": ".",
+    "paths": {
+      "@/*": ["./src/*"],
+      "@components/*": ["./src/components/*"],
+      "@layouts/*": ["./src/layouts/*"],
+      "@styles/*": ["./src/styles/*"],
+      "@content/*": ["./src/content/*"]
+    },
+    "jsx": "react-jsx",
+    "jsxImportSource": "react"
+  },
+  "include": ["src/**/*", ".tina/**/*", "db/**/*"],
+  "exclude": ["node_modules", "dist", ".astro"]
+}