feat: add nginx proxy for theme injection (cleaner approach)

asciinema/theme/inject.js

@@ -0,0 +1,22 @@
+// Inject custom theme CSS and favicon
+(function() {
+  // Inject custom CSS
+  var link = document.createElement('link');
+  link.rel = 'stylesheet';
+  link.href = '/theme/custom.css';
+  document.head.appendChild(link);
+
+  // Inject custom favicon
+  var favicon = document.createElement('link');
+  favicon.rel = 'icon';
+  favicon.type = 'image/svg+xml';
+  favicon.href = '/theme/favicon.svg';
+
+  // Remove existing favicons first
+  var existingFavicons = document.querySelectorAll('link[rel*="icon"]');
+  existingFavicons.forEach(function(el) {
+    el.remove();
+  });
+
+  document.head.appendChild(favicon);
+})();