fix(theme): readable oneOf switcher pills in dark mode
primary.main was #71717a (muted gray) in the dark theme, so the oneOf option pills rendered as a muddy gray fill (active) and faint gray-on-dark text (inactive) — hard to read. Now #3b82f6 (blue), consistent with the light theme's primary. Dark-mode only.
Builds on v2.1.4's schema-title fix.