✨ feat(vscode): 新增第五种工单会话「原型会话」

照测试会话那条链路补一份 prototype：

- 消息与路由：session/start-prototype、session/resume-prototype、
  issue/update-prototype-profile-path，都进只读门禁
- 会话：handleStartPrototypeSession / handleResumePrototypeSession，
  终端名 issue-N-原型；cwd 有 worktree 用 worktree、没有退主仓库根
  （原 resolveTestSessionCwd 改名 resolveWorktreeOrRootCwd 两种会话共用）
- 不要求有 PR，任何阶段都能起；前置工单锁仍然拦
- 提示词：新增 prompts/prototype.md，设置里可改，占位符 {issueNumber}
- profile：工单级 prototypeProfilePath > 设置里的原型默认 profile >
  内置默认，与其它会话互不回退
- 状态字段 prototypeSessionId / prototypeProfilePath / prototypeTabOpen
  贯通 gitea、youtrack、本机 state 与移交包
- 详情面板加「原型会话id」「原型配置文件」两行，设置面板加对应两项

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

vscode/src/panel/handlers/handoff.test.ts

@@ -63,15 +63,17 @@ describe('payloads', () => {
       handoffFrom: 'chw',
     })
   })
-  it('本机墓碑：keepWorktreePath=false 时九个本机字段全清', () => {
+  it('本机墓碑：keepWorktreePath=false 时本机字段全清', () => {
     expect(handoffLocalTombstones({ keepWorktreePath: false })).toEqual({
       sessionId: '',
       implementSessionId: '',
       reviewSessionId: '',
       testSessionId: '',
+      prototypeSessionId: '',
       profilePath: '',
       brainstormProfilePath: '',
       testProfilePath: '',
+      prototypeProfilePath: '',
       worktreePath: '',
       prDiffFile: '',
     })
@@ -84,9 +86,11 @@ describe('payloads', () => {
       implementSessionId: '',
       reviewSessionId: '',
       testSessionId: '',
+      prototypeSessionId: '',
       profilePath: '',
       brainstormProfilePath: '',
       testProfilePath: '',
+      prototypeProfilePath: '',
       prDiffFile: '',
     })
   })
@@ -99,9 +103,11 @@ describe('payloads', () => {
       implementSessionId: null,
       reviewSessionId: null,
       testSessionId: null,
+      prototypeSessionId: null,
       profilePath: null,
       brainstormProfilePath: null,
       testProfilePath: null,
+      prototypeProfilePath: null,
       prDiffFile: null,
       worktreePath: null,
       worktreeExists: false,
@@ -119,9 +125,11 @@ describe('payloads', () => {
       implementSessionId: null,
       reviewSessionId: null,
       testSessionId: null,
+      prototypeSessionId: null,
       profilePath: null,
       brainstormProfilePath: null,
       testProfilePath: null,
+      prototypeProfilePath: null,
       prDiffFile: null,
     })
   })