chore: remove dead debug code — isDevMode, debug CSS, __DEV__ flag

miniprogram/app.wxss

@@ -250,23 +250,3 @@ page {
 .nav-back-light {
   color: rgba(255, 255, 255, 0.9);
 }
-
-.debug-actions {
-  margin-top: 40rpx;
-  padding: 20rpx;
-  background: #fff8e1;
-  border-radius: 12rpx;
-  border: 2rpx dashed #f5a623;
-}
-
-.debug-label {
-  font-size: 24rpx;
-  color: #f5a623;
-  margin-bottom: 16rpx;
-  font-weight: 600;
-}
-
-.debug-actions .btn-sm {
-  margin-top: 12rpx;
-  font-size: 26rpx;
-}