feat: Add dark mode toggle functionality

wiki/darkmode-toggle.js

@@ -0,0 +1,34 @@
+const themeToggleButton = document.getElementById('theme-toggle');
+const themePreferenceKey = 'userThemePreference';
+const darkThemePath = 'wiki/darkmode.css';
+
+function applyTheme(theme) {
+    let link = document.querySelector('link[href="' + darkThemePath + '"]');
+    if (theme === 'dark') {
+        if (!link) {
+            link = document.createElement('link');
+            link.rel = 'stylesheet';
+            link.href = darkThemePath;
+            document.head.appendChild(link);
+        }
+    } else {
+        if (link) {
+            document.head.removeChild(link);
+        }
+    }
+}
+
+function loadTheme() {
+    const savedTheme = localStorage.getItem(themePreferenceKey);
+    applyTheme(savedTheme);
+}
+
+function toggleTheme() {
+    const currentTheme = localStorage.getItem(themePreferenceKey) === 'dark' ? 'light' : 'dark';
+    localStorage.setItem(themePreferenceKey, currentTheme);
+    applyTheme(currentTheme);
+}
+
+themeToggleButton.addEventListener('click', toggleTheme);
+
+loadTheme();