Switch to static output and add Azure SWA deployment

- Set output: 'static' in astro.config.mjs; remove Vercel/Netlify adapters
- Remove API routes (contact, newsletter) incompatible with static mode
- Add Azure SWA deploy workflow using @azure/static-web-apps-cli via npx
- Add public/staticwebapp.config.json for SWA routing and 404 fallback

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -40,10 +40,8 @@
   },
   "dependencies": {
     "@astrojs/mdx": "5.0.0",
-    "@astrojs/netlify": "^7.0.2",
     "@astrojs/react": "5.0.0",
     "@astrojs/sitemap": "^3.7.1",
-    "@astrojs/vercel": "^10.0.0",
     "@fontsource-variable/jetbrains-mono": "^5.2.8",
     "@fontsource-variable/manrope": "^5.2.8",
     "@fontsource-variable/outfit": "^5.2.8",