修复深色与浅色主题无法切换的问题

修正 CSS 选择器避免 :root 始终应用深色变量，并改进 theme.js 点击绑定与首屏主题恢复。

Co-authored-by: Cursor <cursoragent@cursor.com>

static/js/theme.js

@@ -33,13 +33,21 @@
         apply(prefersLight ? 'light' : 'dark');
     }
 
-    document.addEventListener('DOMContentLoaded', function () {
+    document.addEventListener('click', function (e) {
+        var btn = e.target.closest('[data-theme-pick]');
+        if (!btn) return;
+        e.preventDefault();
+        apply(btn.getAttribute('data-theme-pick'));
+    });
+
+    function syncButtons() {
         var cur = document.documentElement.getAttribute('data-theme') || 'dark';
         updateButtons(cur);
-        document.querySelectorAll('[data-theme-pick]').forEach(function (btn) {
-            btn.addEventListener('click', function () {
-                apply(btn.getAttribute('data-theme-pick'));
-            });
-        });
-    });
+    }
+
+    if (document.readyState === 'loading') {
+        document.addEventListener('DOMContentLoaded', syncButtons);
+    } else {
+        syncButtons();
+    }
 })();