⚡ 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/issueLock.ts

@@ -0,0 +1,25 @@
+import type { Issue } from '../gitea/types'
+
+export interface LockedReason {
+  locked: boolean
+  prerequisiteNumber?: number
+  prerequisiteColumn?: string
+}
+
+/**
+ * 纯判定：工单被未完成的前置挡住才算锁定。快照里找不到工单或前置一律放行，
+ * 与 webview 的 `isIssueLocked` 保持同一语义。
+ */
+export function evaluateLockedReason(issues: Issue[], issueNumber: number): LockedReason {
+  const issue = issues.find(i => i.number === issueNumber)
+  if (!issue || issue.prerequisite === undefined)
+    return { locked: false }
+  const prereq = issues.find(i => i.number === issue.prerequisite)
+  if (!prereq || prereq.column === 'done')
+    return { locked: false }
+  return {
+    locked: true,
+    prerequisiteNumber: prereq.number,
+    prerequisiteColumn: prereq.column,
+  }
+}