🐛 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/webview-ui/src/lib/messages.ts

@@ -80,6 +80,7 @@ export interface ProfilesData {
 
 export type ExtensionToWebview
   = | { type: 'issues/loading' }
+    | { type: 'issues/loaded' }
     | { type: 'issues/update', issues: Issue[], scope: 'mine' | 'all', globalAutoReview: boolean, youtrackConfigured: boolean, me?: string, avatars?: Record<string, string> }
     | { type: 'issues/error', message: string }
     | { type: 'issue/patch', issueNumber: number, patch: { autoReview?: boolean, specFile?: string, planFile?: string, prDiffFile?: string | null, sessionId?: string | null, implementSessionId?: string | null, reviewSessionId?: string | null, reviewSessionFileExists?: boolean, testSessionId?: string | null, pr?: string | null, implementStatus?: 'running' | 'done' | 'failed' | null, column?: IssueColumn, worktreePath?: string | null, prMerged?: boolean, prMergedAt?: string | null, branch?: string | null, color?: string, worktreeExists?: boolean, brainstormTabOpen?: boolean, implementTabOpen?: boolean, reviewTabOpen?: boolean, testTabOpen?: boolean, profilePath?: string | null, brainstormProfilePath?: string | null, testProfilePath?: string | null, assignees?: string[], handoffAttachmentId?: string | null, handoffFrom?: string | null } }