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>

astro.config.mjs

@@ -4,13 +4,9 @@ import sitemap from '@astrojs/sitemap';
 import react from '@astrojs/react';
 import icon from 'astro-icon';
 import tailwindcss from '@tailwindcss/vite';
-import vercel from '@astrojs/vercel';
-import netlify from '@astrojs/netlify';
-
-const isNetlify = process.env.DEPLOY_TARGET === 'netlify';
 
 export default defineConfig({
-  adapter: isNetlify ? netlify() : vercel(),
+  output: 'static',
   site: process.env.SITE_URL || 'https://example.com',
 
   env: {
@@ -52,10 +48,6 @@ export default defineConfig({
     },
   },
 
-  security: {
-    checkOrigin: true,
-  },
-
   markdown: {
     shikiConfig: {
       theme: 'github-dark',