fix(favicon): dynamic favicon switching based on color scheme in js (#735)

* fix(favicon): dynamic favicon switching based on color scheme in js

* refactor(favicon): simplify favicon logic and ensure dynamic switching based on color scheme

* docs(favicon): enhance favicon setup instructions with dark mode support and adaptive SVG guidance

assets/js/favicon.js

@@ -0,0 +1,22 @@
+// {{ $faviconDarkExists := fileExists (path.Join "static" "favicon-dark.svg") }}
+(function () {
+  const faviconEl = document.getElementById("favicon-svg");
+  const faviconDarkExists = "{{ $faviconDarkExists }}" === "true";
+
+  if (faviconEl && faviconDarkExists) {
+    const lightFavicon = '{{ "favicon.svg" | relURL }}';
+    const darkFavicon = '{{ "favicon-dark.svg" | relURL }}';
+
+    const darkModeQuery = window.matchMedia("(prefers-color-scheme: dark)");
+
+    function updateFavicon(e) {
+      faviconEl.href = e.matches ? darkFavicon : lightFavicon;
+    }
+
+    // Set favicon on load
+    updateFavicon(darkModeQuery);
+
+    // Listen for system preference changes
+    darkModeQuery.addEventListener("change", updateFavicon);
+  }
+})();