Native Windows launch portability for spawned CLIs

[nillo]

Problem

ContextRelay launches external CLIs directly with Node/Bun spawn/execFileSync. On native Windows, npm-installed tools such as codex, claude, git, and tmux are resolved as .cmd shims, which direct spawn/execFileSync calls do not execute the same way as real binaries. This can fail ctxrelay claude/codex/pair on native Windows.

Evidence

• src/cli/claude.ts:58
• src/cli/codex.ts:203
• src/cli/codex.ts:250
• src/codex-adapter.ts:185
• src/codex-adapter.ts:197
• src/codex-adapter.ts:706

Candidate fixes

• Resolve commands through PATHEXT on win32 and execute the resolved .cmd/.exe safely, or
• Use shell:true with windowsHide:true only on win32, with explicit argument-quoting tests.

Validation needed

• Add Windows CI coverage for the launch paths.
• Run a real native-Windows smoke for ctxrelay claude, ctxrelay codex, and ctxrelay pair.

Notes

v1.2.1 documents macOS/Linux/WSL support and leaves native-Windows launch portability as this follow-up.