[Torgh]

Summary

Settings → Appearance now offers 🖥️ System (default, the previous behaviour), ☀️ Light and 🌙 Dark.

• Saved per browser (localStorage), applied by an inline <head> script before the first paint – no flash of the wrong theme on reload, as in Next's Preventing flash before hydration guide. ThemeAgent re-applies it after React's dev-mode remount.
• Colour tokens in globals.css now use light-dark(light, dark); data-theme on <html> only sets color-scheme, so every colour is still defined once.
• The Google map is created in the chosen scheme (it only reads the scheme at creation, so it is re-created on change). The OpenStreetMap map keeps its light style, as before.
• The printable itinerary stays light whatever the theme.
• Other tabs and OS light/dark switches are picked up live.

lib/theme.ts holds the pure parts (tested); lib/useTheme.ts the browser hooks, excluded from coverage like lib/hooks.ts.

Test plan

• bun run typecheck, lint, test:coverage (169 tests), build
• In Chrome (Playwright): Dark applies at once and survives a reload, also with the app's JS blocked (the <head> script alone sets it); Light wins over a dark OS; System follows the OS and clears the saved value
• Trip board and Google map in dark mode

🤖 Generated with Claude Code