🐛 fix(vscode): 刷新按钮加载态可见，图标随重拉转圈

刷新按钮此前只发消息重拉数据，看板已有列表时界面毫无变化，用户
无法判断点击是否生效。消息协议里的 issues/loading 从未被发送。

loadAndPush 现在在开跑前推 issues/loading，并在 finally 里推新增的
issues/loaded，保证成功、报错、缺 token 提前返回都能收尾；webhook
触发的自动重拉同样走这条链路。webview 据此维护 refreshing 状态，
刷新图标转圈并在期间禁用按钮。

Claude-Session: https://claude.ai/code/session_01REdhpbaNyqWASF2HWsnTFv

vscode/package.json

@@ -2,7 +2,7 @@
   "publisher": "clurdra",
   "name": "superpowers-vscode-clurdra",
   "displayName": "Superpowers-clurdra",
-  "version": "0.2.125",
+  "version": "0.2.126",
   "packageManager": "pnpm@10.27.0",
   "description": "Superpowers specs and plans Kanban explorer",
   "author": "clurdra",