Improve system theme and appearance settings

[bakuur]

Summary

• Add a Preferences appearance setting (System / Light / Dark) and apply it at startup via wx.App.SetAppearance.
• Replace hardcoded light-gray/white control backgrounds with system colors so preference fields and ship-browser buttons follow the active theme.
• Allow dark-mode detection on Windows (gui.utils.dark.isDark no longer short-circuits on wxMSW).
• Bump wxPython from 4.2.1 to 4.3.0 so appearance APIs are available.
• Ignore the local run.ps1 launcher so it is not committed.

Test plan

• Start Pyfa on Windows and confirm it launches with the default System appearance.
• Preferences -> General: switch Appearance to Dark, restart, confirm the UI uses a dark theme.
• Switch to Light, restart, confirm a light theme.
• Check Database and Logging preference path fields, plus ship-browser bitmap buttons, for readable backgrounds in both themes.
• Confirm existing fittings and graphs still open after the wxPython 4.3.0 bump.

[bakuur]