feat: integrate 5 feature branches + daemon/job 命令层级化 + 跨平台后台引擎 + TypeScript 错误修复

Squashed merge of:
1. fix/mcp-tsc-errors — 修复上游 MCP 重构后的 tsc 错误和测试失败
2. feat/pipe-mute-disconnect — Pipe IPC 逻辑断开、/lang 命令、mute 状态机
3. feat/stub-recovery-all — 实现全部 stub 恢复 (task 001-012)
4. feat/kairos-activation — KAIROS 激活解除阻塞 + 工具实现
5. codex/openclaw-autonomy-pr — 自治权限系统、运行记录、managed flows

Additional:
6. daemon/job 命令层级化重构 (subcommand 架构)
7. 跨平台后台引擎抽象 (detached/tmux engines)
8. 修复 src/ 中 43 个预存在的 TypeScript 类型错误
9. 修复 langfuse isolated test mock 完整性
10. 修复 CodeRabbit 审查的 Critical/Major/Minor 问题
11. remote-control-server logger 抽象 (测试 stderr 静默化)
12. /simplify 审查修复 (代码复用、质量、效率)

src/cli/bg/engine.ts

@@ -0,0 +1,47 @@
+/**
+ * BgEngine — cross-platform background session engine abstraction.
+ *
+ * Implementations:
+ *   TmuxEngine    — macOS/Linux with tmux installed
+ *   DetachedEngine — Windows, or macOS/Linux without tmux (fallback)
+ */
+
+export interface SessionEntry {
+  pid: number
+  sessionId: string
+  cwd: string
+  startedAt: number
+  kind: string
+  name?: string
+  logPath?: string
+  entrypoint?: string
+  status?: string
+  waitingFor?: string
+  updatedAt?: number
+  bridgeSessionId?: string
+  agent?: string
+  tmuxSessionName?: string
+  engine?: 'tmux' | 'detached'
+}
+
+export interface BgStartOptions {
+  sessionName: string
+  args: string[]
+  env: Record<string, string | undefined>
+  logPath: string
+  cwd: string
+}
+
+export interface BgStartResult {
+  pid: number
+  sessionName: string
+  logPath: string
+  engineUsed: 'tmux' | 'detached'
+}
+
+export interface BgEngine {
+  readonly name: 'tmux' | 'detached'
+  available(): Promise<boolean>
+  start(opts: BgStartOptions): Promise<BgStartResult>
+  attach(session: SessionEntry): Promise<void>
+}