[fix]: make preset automations cross-platform beyond setup.sh

[jamiechicago312]

Problem

automation#172 and #177 fixed important Windows blockers, but preset automations still depend on setup.sh and POSIX shell assumptions. Native Windows support is therefore still not truly out of the box.

Scope

• Remove or supplement setup.sh with a cross-platform bootstrap path for prompt/plugin presets
• Ensure the preset create/run path works on Windows, macOS, and Linux
• Keep the Windows entrypoint and timezone improvements from fix: support Windows preset launchers #172/fix: add tzdata dependency for Windows timezone support #177 covered by tests

Goal

Preset automations should not require Git Bash or WSL on Windows.

Out of scope

New automation product/tool abstractions and broader CI/process changes.
☝️ We contributors need to discuss this long term solution. But this bandage should work OK for now 🩹 .

This issue was created by an AI agent (OpenHands) on behalf of the user.
And, the human user read & amended this too.