fix(win): hide the console window for background child processes

[Aikiooo]

What

On Windows, Node allocates a console window for a child process unless windowsHide is set. That window flashes on screen and can take focus away from whatever the user is doing. For the agent processes, which live for the whole session, it happens on every start.

process-scanner.ts already passes the option. The other background call sites did not, so this sets it on the ones whose output is captured:

File	Command
agents/base.ts	the ACP agent subprocess
agents/codex-readonly.ts	app-server --stdio
filesystem/index.ts	git show HEAD:<path> for diffs
notify.ts	the desktop notification helper
ports.ts	netstat, findstr, taskkill (the win32 branches)
update-and-start.ts	npm list -g shellular
update-runner.ts	the detached self-update worker
utils.ts	where in commandExists

Left alone on purpose

• stdio: "inherit" spawns in daemon.ts and update-and-start.ts. pm2 startup prints the sudo command the user has to read and re-run, so those windows must stay visible. Hiding them would hide output the user needs.
• POSIX-only branches ÔÇö lsof, /bin/sh, and the login shell used for command -v ÔÇö plus macOS caffeinate. The option does nothing there, so adding it would be noise.
• terminal/index.ts spawns through node-pty, which exposes no option for this on Windows. Worth knowing: node-pty's own kill() forks a helper to enumerate the console process list without windowsHide, so closing a terminal can flash a window regardless of this change. That one belongs upstream in microsoft/node-pty, not here.

Risk

None off Windows: windowsHide maps to CREATE_NO_WINDOW and Node ignores it on other platforms. Every site changed here has its output captured, so nothing that a caller reads goes away.

Tests

The cli package has no test setup, and this is a spawn-option change, so I did not add a test rather than introduce a framework here. tsc and biome check are clean.

Note

I cannot verify the window behaviour itself from this machine beyond the reasoning above; the option's semantics are documented, but I did not observe a console window with and without it.