feat(h5): SGBridge 新增 closePage(返回上一页)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

h5/shared/bridge.js

@@ -118,6 +118,12 @@
     else console.log('[SGBridge mock] launchApp →', json);
   }
 
+  /** 网页请求返回上一页(原生 popBackStack;无桥时浏览器仅 log)。 */
+  function closePage() {
+    if (hasNative && native.closePage) native.closePage();
+    else console.log('[SGBridge mock] closePage');
+  }
+
   // ====== 原生 → H5 事件总线 ======
 
   var listeners = {}; // event → [fn]
@@ -155,6 +161,7 @@
     startCompare: startCompare,
     startCouponClaim: startCouponClaim,
     launchApp: launchApp,
+    closePage: closePage,
     // 事件
     on: on,
     _emit: _emit,