feat: SEO improvements — related content, IndexNow, manifest, llms.txt

- Enable showRelatedContent + showSummary in article config
- Add IndexNow ping step to CI deploy pipeline
- Fix site.webmanifest branding (was Congo, now Internet for Kids)
- Update llms.txt to include French language section

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

static/site.webmanifest

@@ -0,0 +1,21 @@
+{
+  "name": "Internet for Kids",
+  "short_name": "IFK",
+  "description": "Expert insights on child protection laws, online safety, and digital family protection worldwide.",
+  "start_url": "/en/",
+  "display": "standalone",
+  "background_color": "#ffffff",
+  "theme_color": "#1a365d",
+  "icons": [
+    {
+      "src": "/android-chrome-192x192.png",
+      "sizes": "192x192",
+      "type": "image/png"
+    },
+    {
+      "src": "/android-chrome-512x512.png",
+      "sizes": "512x512",
+      "type": "image/png"
+    }
+  ]
+}