feat: 完成 M2 mosh（LAN + tsnet 端到端验证）

- mosh(blinksh/ios C++)+protobuf-lite 交叉编译为 MoshCore.xcframework
  （CommonCrypto 后端、含 arm64 模拟器 slice；绕 autotools 用 CMake 直编 + 手写 config.h）
- tsnet 桥新增 UDP relay（StartMoshRelay：loopback↔tsnet.Dial 逐包搬运）
- MoshSession（pipe↔FILE*/pthread/SIGWINCH）+ MoshConnectScanner（TXCore，+4 单测=39）
- SSHTerminalModel 编排：SSH 引导 mosh-server→解析 MOSH CONNECT→relay→mosh 接管
- LAN 直连 + mosh-over-tsnet 均端到端验证通过，R1(tsnet UDP 数据报语义) 证伪

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vendor/mosh/README.md

@@ -0,0 +1,15 @@
+#iOSClient for Mosh
+These are a set of small changes to make Mosh compile for iOS as
+a separate library that can be linked into applications. Please do
+not use to compile mosh-client or mosh-server. You can use a separate
+script [Build Mosh](https://github.com/blinksh/build-mosh) and it is
+currently being used in [Blink](https://github.com/blinksh/blink).
+
+There are four main changes to the original Mosh code, that we hope to
+integrate at some point with the main branch:
+- iOSClient as a new main loop for the library.
+- Multithread code suppport.
+- Makefiles support for the iOS version.
+- Bug fixes (sockets, etc...)
+
+Original Mosh can be found on [Mosh](https://github.com/mobile-shell/mosh)