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>

public/staticwebapp.config.json

@@ -0,0 +1,15 @@
+{
+  "navigationFallback": {
+    "rewrite": "/404.html",
+    "exclude": ["/assets/*", "/fonts/*", "/_astro/*", "*.ico", "*.png", "*.jpg", "*.svg", "*.webp", "*.webmanifest", "*.xml", "*.txt"]
+  },
+  "trailingSlash": "auto",
+  "mimeTypes": {
+    ".json": "application/json"
+  },
+  "responseOverrides": {
+    "404": {
+      "rewrite": "/404.html"
+    }
+  }
+}