fix(ai-tools): detect AI CLIs on Windows through PATHEXT

which() looked for the bare name only, so on Windows every tool (claude.exe,
codex.cmd, ...) read installed: false. It now tries each PATHEXT extension
(default .EXE;.CMD;.BAT), the bare name only when it already carries one -
npm's extensionless shim beside codex.cmd is a sh script Windows cannot run.

spawnTarget() gives a .cmd/.bat shell: true and a quoted path, used by the
install/update job runner and the npm/version probes, which Node otherwise
refuses with EINVAL (CVE-2024-27980). Catalog argv only.

INSTALL.md

@@ -54,6 +54,9 @@ sudo pacman -S git tmux          # Arch
 
 Windows has no native tmux. Run AgentHub under **WSL2** and install it inside
 the WSL distro — a tmux from Git Bash or MSYS is not what the server executes.
+On a native Windows install, workspace terminals are unavailable, but Settings →
+Agents still detects each AI CLI through `PATHEXT` (`claude.exe`, `codex.cmd`)
+and runs a `.cmd` updater or npm through `cmd.exe`.
 
 A terminal pane gets a draggable scrollbar only on **tmux 3.7+** — older
 versions work, just without it, and `/agenthub-doctor` warns. Homebrew ships the