Adds 16 unit tests covering the light/dark terminal detection path
introduced in the previous commit:
- Env override priority (HERMES_LIGHT, HERMES_TUI_LIGHT,
HERMES_TUI_THEME, HERMES_TUI_BACKGROUND, COLORFGBG)
- Detection cache stickiness
- _maybe_remap_for_light_mode() no-op in dark mode
- Known dark-mode color remap (#FFF8DC -> #1A1A1A etc)
- Case-insensitive lookup
- Unknown color passthrough
- Status-bar paired colors (#C0C0C0, #888888, #555555, #8B8682) are
intentionally NOT remapped — regression guard for the patch-11 fix,
since remapping them would produce dark-on-dark on the status bar's
navy bg
- SkinConfig.get_color() wrapper is installed and idempotent
- SkinConfig.get_color() does remap in light mode and passes through
in dark mode
We don't try to fake an OSC 11 reply — that path is exercised
end-to-end in real Terminal.app; the env-override path covers the
algorithmic logic.
