New files: AppTheme (palette + env key), ThemeManager (Observable singleton,
UserDefaults persistence). Themes: Default, Emacs, Dracula, One Dark,
Monokai, Material. Each controls background, accent, text, code block
colors and a highlight.js theme for syntax highlighting.
RootView applies preferredColorScheme, tint and appTheme env to the root
group. SettingsView applies the same modifiers to its NavigationStack so
the modal sheet is themed immediately (sheets run in a separate UIWindow
and don't inherit preferredColorScheme from the parent hierarchy).
Theme selection in Settings uses onTapGesture instead of buttonStyle(.plain)
inside Form, which was silently intercepting the button action.
CodeBlockView, TimelineView, NotificationsView all read from appTheme env.
andros
d2ab6ea377