Dark mode

Orbi now ships a proper dark theme across the coach dashboard and the client app:

• Light, Dark, or System. Coaches set it in Settings → Appearance; clients in More → Appearance. "System" follows your device's light/dark setting automatically. Your choice is remembered on that browser.
• Everything adapts. Pages, cards, charts, tables, menus, and status colors all respond to the theme — including the revenue and progress charts.
• Light stays the default. Nothing changes unless you opt in.