✨ feat(vscode): 头脑风暴会话可清除，悬停提示改窄改紧凑

工单记着的头脑风暴会话 id 此前没有清除入口，续聊只能 resume 旧会话，
把几个版本前的提示词和它当时报的错一起带回来。会话 id 行新增清除按钮，
确认后把 state JSON 的 sessionId 置空，下次续聊新开会话；会话文件不动，
手上有 id 仍可 claude --resume 找回。

悬停气泡此前贴着视口右边测量尺寸：fixed 元素的可用宽度是「视口宽 - left」，
贴边测会被挤窄、行数变多，按那个高度定位就浮高一截。改成先在左上角量再落位，
字号行高收紧，提示文案压成一行。顺带修掉「重置为待办」的错误说明——它会停
会话、删 worktree 和未合并 PR，不是原样保留。

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

vscode/webview-ui/src/hooks/useIssues.ts

@@ -230,6 +230,8 @@ export interface UseIssuesResult {
    * postMessage 持久化到 state JSON。失败时扩展端 push `issue/patch` 回滚。
    */
   updateIssueBrainstormProfilePath: (issueNumber: number, brainstormProfilePath: string) => void
+  /** 清掉工单记的头脑风暴会话 id，下次续聊新开会话。 */
+  clearBrainstormSession: (issueNumber: number) => void
   /**
    * 覆盖该工单测试会话专用的 Claude 配置文件，乐观更新本地 state 后
    * postMessage 持久化到 state JSON。失败时扩展端 push `issue/patch` 回滚。
@@ -652,6 +654,12 @@ export function useIssues(): UseIssuesResult {
     postMessage({ type: 'issue/update-brainstorm-profile-path', issueNumber, brainstormProfilePath })
   }, [])
 
+  // 清除头脑风暴会话 id：扩展侧先弹确认框，确认后才落库并推 issue/patch，
+  // 所以这里不做乐观更新。
+  const clearBrainstormSession = useCallback((issueNumber: number): void => {
+    postMessage({ type: 'issue/clear-brainstorm-session', issueNumber })
+  }, [])
+
   const updateIssueTestProfilePath = useCallback((issueNumber: number, testProfilePath: string): void => {
     // Optimistically update local state so the dropdown reflects immediately
     // without remounting the issues list / detail panel via a full reload.
@@ -930,5 +938,5 @@ export function useIssues(): UseIssuesResult {
     return cleanup
   }, [clearPrDiffSummaryRunning, markHandoffRunning])
 
-  return { state, settings, avatars, globalAutoReview, youtrackConfigured, importYouTrack, toasts, profiles, setIssues, refresh, refreshing, scope, toggleScope, saveSettings, listYouTrackProjects, youtrackProjects, dismissSettings, requestEditAuth, createIssue, dismissToast, openUrl, resumeSession, resumeReviewSession, startTestSession, resumeTestSession, focusSession, openFile, implement, generatePrDiffSummary, isPrDiffSummaryRunning, openPr, openWorktree, deleteWorktree, mergeBranch, deleteIssue, closeIssue, closeSessionTab, continueBrainstorm, changeColumn, setDependency, clearDependency, updateIssueAutoReview, updateIssueProfilePath, updateIssueBrainstormProfilePath, updateIssueTestProfilePath, logs, fetchLogs, clearLogs, pendingSelectId, clearPendingSelect, commitRunning, runCommit, hasChanges, release, runRelease, cherryPick, dismissCherryPick, confirmCherryPick, envLocked, envFileCount, envLockRunning, envLockTitle, toggleEnvLock, me, handoffUsers, requestHandoffUsers, startHandoff, acceptHandoff, isHandoffRunning }
+  return { state, settings, avatars, globalAutoReview, youtrackConfigured, importYouTrack, toasts, profiles, setIssues, refresh, refreshing, scope, toggleScope, saveSettings, listYouTrackProjects, youtrackProjects, dismissSettings, requestEditAuth, createIssue, dismissToast, openUrl, resumeSession, resumeReviewSession, startTestSession, resumeTestSession, focusSession, openFile, implement, generatePrDiffSummary, isPrDiffSummaryRunning, openPr, openWorktree, deleteWorktree, mergeBranch, deleteIssue, closeIssue, closeSessionTab, continueBrainstorm, changeColumn, setDependency, clearDependency, updateIssueAutoReview, updateIssueProfilePath, updateIssueBrainstormProfilePath, clearBrainstormSession, updateIssueTestProfilePath, logs, fetchLogs, clearLogs, pendingSelectId, clearPendingSelect, commitRunning, runCommit, hasChanges, release, runRelease, cherryPick, dismissCherryPick, confirmCherryPick, envLocked, envFileCount, envLockRunning, envLockTitle, toggleEnvLock, me, handoffUsers, requestHandoffUsers, startHandoff, acceptHandoff, isHandoffRunning }
 }