Replace useSetting()-based useTheme() with a React context (ThemeProvider
+ useTheme/usePaletteControl). The context holds palette key in state so
pressing a palette button in Settings re-renders all screens instantly.
Persists to SQLite and reloads the stored value on mount.
- theme.ts: useTheme() hook with race calendar (May–Sep windows),
auto-detects Giro/Tour/Vuelta by date; stores override in SQLite
- All screens (feed, import, activity, tab bar) now use accent/dim
from useTheme() instead of hardcoded #60a5fa
- Settings: Palette section with Auto/Default/Giro/Tour/Vuelta buttons
to override the auto-detected palette for testing
Davide Scaini