⚡ perf(vscode): 开会话去掉多余远程往返，spinner 跟随真实进度

开会话原先要先全量拉工单（含每张工单的评论、依赖、PR）做前置锁检查，
再各读一次 state JSON 给 pre-create 钩子和终端图标，几秒后才 createTerminal。

- 锁检查改用主进程已算好的工单快照，快照里没有该工单才回落全量拉取
- state JSON 一次读两处用，且提前发起与本地准备重叠
- 会话行 spinner 由扩展的 session/tab-settled 消息驱动，不再是固定 1.5s 假动画，
  消息丢失时 60s 超时兜底

Claude-Session: https://claude.ai/code/session_01Kgmb1LvrPmFX3NoUDB4zZC

vscode/src/panel/messages.ts

@@ -53,6 +53,8 @@ export type ExtensionToWebview
     | { 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 } }
+    /** 某个会话 id 的开 tab 请求已处理完（开成、复用或被拒都算），webview 据此停掉行内 spinner。 */
+    | { type: 'session/tab-settled', sessionId: string }
     | { type: 'issue/pr-diff-summary-done', issueNumber: number }
     | { type: 'handoff/users-result', issueNumber: number, users: string[] }
     | { type: 'handoff/done', issueNumber: number }