🎨 fix(theme): default theme font preset falls back to Sans instead of Serif

Adjust PRESET_DEFAULT_FONT so that the shipped 'default' preset falls back to the humanist 'sans' (Public Sans) out-of-the-box instead of forcing the editorial 'serif' (Lora). Keeps the 'anthropic' preset on 'serif' as intended.

web/default/src/lib/theme-customization.ts

@@ -170,7 +170,7 @@ export const THEME_COOKIE_KEYS = {
 export const PRESET_DEFAULT_FONT: Partial<
   Record<ThemePreset, ResolvedThemeFont>
 > = {
-  default: 'serif',
+  default: 'sans',
   anthropic: 'serif',
 }