Fix macOS collector Tk crash and clarify Apple silicon setup

[ZhiyuanMa2017]

Summary

This PR improves the macOS collector flow in two ways:

1. Fixes the macOS startup crash caused by Tk/AppKit window creation on a background thread.
2. Clarifies the macOS setup instructions for Homebrew Python on Apple silicon, where tkinter may be missing unless the matching Tk package is installed.

What Changed

Code

• Disable the Tk overlay path on macOS.
• Fall back to terminal input for task descriptions on macOS.
• Skip the Tk screen-selection dialog on macOS.

Docs

• Update the macOS README section to explain that users need a Python installation with Tk support.
• Add a Homebrew example:
  • brew install python-tk@3.14

Why

On macOS, the collector was crashing at startup with:

NSWindow should only be instantiated on the main thread!

This came from the Tk overlay and dialog flow being created from a background thread.

Before that, on Homebrew Python 3.14, tkinter was also missing until the matching Tk package was installed:

ModuleNotFoundError: No module named '_tkinter'

Result

• The collector can now start on macOS without the Tk/AppKit crash.
• macOS users have clearer setup instructions when using Homebrew Python on Apple silicon.

Notes

• macOS users still need to grant:
  • Screen Recording
  • Accessibility

to the terminal app they use to launch the collector.

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Better test this change on windows and linux before merge.