fix: bottom bar safe-area adaptation (height → min-height)

Affected pages:
- order-detail: bottom action bar
- card-buy: bottom price/pay bar
- reserve-index: bottom submit bar

Root cause: box-sizing:border-box + fixed height + padding-bottom:safe-area
caused buttons to overflow when safe area inset is large (iPhone X+).
Changed to min-height so bar expands naturally.

Co-Authored-By: Claude <noreply@anthropic.com>

src/pages/order/order-detail.vue

@@ -532,7 +532,7 @@ $bar-height: 120rpx;
   bottom: 0;
   width: 100%;
   box-sizing: border-box;
-  height: $bar-height;
+  min-height: $bar-height;
   background: $color-card;
   display: flex;
   align-items: center;