Mobile-responsive dashboard, dark mode by default

The dashboard now opens in dark mode unless your OS asks for light, and every page works on a phone. Tables collapse to cards, dialogs stop clipping, and tap targets meet the 44 by 44 minimum.

Last Price is something people open from email and Slack, often on mobile. The dashboard now expects that.

Dark mode is the default, with `prefers-color-scheme: light` still honored

Every page tested at 375px (phone), 768px (tablet), 1280px (desktop)

Tables that used to overflow now either reflow as cards below the `md` breakpoint or scroll inside a contained wrapper

Dialogs and sheets render full-width on small screens with scrollable content areas

All interactive elements meet the 44 by 44 pixel tap-target minimum

Charts use a responsive container so they fit any width without blowing out the page