COLORFGBG reflects the actual terminal profile colors, while
detectMacOSAppearance() reports the OS-level dark/light setting.
When a user runs a dark terminal on macOS light mode (or vice versa),
COLORFGBG gives the correct answer. The previous ordering caused omp
to load the light theme in dark terminals when macOS was in light mode.
Detection priority is now:
1. Mode 2031 (terminal DSR) - most authoritative
2. COLORFGBG env var - reflects terminal profile
3. macOS system appearance - OS-level fallback
4. Default to dark
