✨ feat(vscode): state JSON 新增 handoffAttachmentId/handoffFrom，Issue 透出 assignees

Claude-Session: https://claude.ai/code/session_011cEyL6k351U2BzX1Qmygph

vscode/src/youtrack/stateComment.ts

@@ -20,7 +20,7 @@ import { addComment, listComments } from './api'
 export const STATE_MARKER = '<!--spx-state-->'
 
 /** Same field set as the Gitea state blob — kept independent to avoid coupling. */
-const KNOWN_STATE_FIELDS = ['column', 'sessionId', 'implementSessionId', 'reviewSessionId', 'testSessionId', 'profilePath', 'brainstormProfilePath', 'testProfilePath', 'specFile', 'planFile', 'prDiffFile', 'pr', 'prMerged', 'prMergedAt', 'branch', 'worktreePath', 'implementStatus', 'color', 'autoReview'] as const
+const KNOWN_STATE_FIELDS = ['column', 'sessionId', 'implementSessionId', 'reviewSessionId', 'testSessionId', 'profilePath', 'brainstormProfilePath', 'testProfilePath', 'specFile', 'planFile', 'prDiffFile', 'pr', 'prMerged', 'prMergedAt', 'branch', 'worktreePath', 'implementStatus', 'color', 'autoReview', 'handoffAttachmentId', 'handoffFrom'] as const
 
 /**
  * Parse a comment body into a state object, or null if it isn't a state