Refactor navigation to Tabs+Languages, add contact page and Inter font

Switch primary navigation to Tabs containing Languages for multi-topic
extensibility. Add contact page with project links, issue reporting,
and contribution guide. Set Inter as the sans-serif font for English
text and add custom CSS for description sizing and logo rendering.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.claude/settings.local.json

@@ -0,0 +1,7 @@
+{
+  "permissions": {
+    "allow": [
+      "WebSearch"
+    ]
+  }
+}