feat: pages contenu + SEO + Umami + sitemap

- Pages /a-propos, /mentions-legales, /dependances, /soutenir (Ko-fi)
- Header/footer enrichis (lien Soutenir, mentions, API publique)
- @astrojs/sitemap + /sitemap-departements.xml.ts (96 dépts)
- robots.txt + og-image.svg + JSON-LD Schema.org
- Meta tags Open Graph + Twitter Card + canonical
- Umami snippet conditionnel (UMAMI_WEBSITE_ID env)
- Slot SENTRY_DSN dans .env.tmpl (GlitchTip — SDK à wire ultérieurement)
- @tailwindcss/typography pour les pages contenu

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

astro.config.mjs

@@ -1,11 +1,20 @@
 import { defineConfig } from 'astro/config';
 import node from '@astrojs/node';
 import tailwind from '@astrojs/tailwind';
+import sitemap from '@astrojs/sitemap';
 
 export default defineConfig({
   output: 'server',
   adapter: node({ mode: 'standalone' }),
-  integrations: [tailwind({ applyBaseStyles: false })],
+  integrations: [
+    tailwind({ applyBaseStyles: false }),
+    sitemap({
+      filter: (page) =>
+        !page.includes('/api/') &&
+        !page.includes('/departement/'),
+      // /departement/* est dynamique pour les 96 dépts — généré dans /sitemap-departements.xml.ts à part.
+    }),
+  ],
   server: { host: '0.0.0.0', port: 4321 },
   site: 'https://info-canicule.nocleus.com',
   vite: {