feat: scaffold Astro 7 with Tailwind 4, MDX, sitemap, node adapter and tooling

- Tailwind v4 via @tailwindcss/vite + typography plugin
- astro-icon (Tabler), self-hosted Rubik/Inter, RSS, Pagefind postbuild
- Prettier (astro + tailwind plugins), editorconfig
- new:post script with Turkish-aware slugify

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.prettierrc.json

@@ -0,0 +1,7 @@
+{
+  "singleQuote": true,
+  "printWidth": 100,
+  "plugins": ["prettier-plugin-astro", "prettier-plugin-tailwindcss"],
+  "tailwindStylesheet": "./src/styles/global.css",
+  "overrides": [{ "files": "*.astro", "options": { "parser": "astro" } }]
+}