fix: 背景改为不透明，保持Dream2.0主题色和圆角

web/src/App.vue

@@ -18,7 +18,7 @@ onMounted(() => {
 <style>
 /* ─── Light Mode (Dream2.0 Plus style) ─── */
 :root {
-  --page-bg: rgba(255, 255, 255, 0.94);
+  --page-bg: #f5f7fa;
   --card-bg: #ffffff;
   --card-hover: #f2f6fc;
   --sidebar-bg: #ffffff;
@@ -51,9 +51,9 @@ onMounted(() => {
 
 /* ─── Dark Mode (Dream2.0 Plus night style) ─── */
 html.dark {
-  --page-bg: rgba(40, 44, 52, 0.6);
-  --card-bg: rgba(40, 44, 52, 0.8);
-  --card-hover: rgba(40, 44, 52, 0.9);
+  --page-bg: #282c34;
+  --card-bg: #3a3f4b;
+  --card-hover: #4a5060;
   --sidebar-bg: #010409;
   --text-primary: #ccc;
   --text-secondary: #8b949e;