Revamp App

[zaelgohary]

Changes

• add design tokens and theme (light/dark) with explicit text colors
• introduce base widgets: AppScaffold, AppButton, AppCard (borders, margins)
• set up go_router and route config; switch to MaterialApp.router
• create Home, Peers, Settings screens; Peers detail bottom sheet
• Riverpod state: app settings (ThemeMode with persistence) and mycelium providers
• MyceliumService: start/stop, status stream, peers persistence
• fix Android Kotlin plugin mismatch (1.9.24) in android/settings.gradle
• remove legacy global scaffold in main.dart; render routed screens directly
• Home: replace Expanded-in-ListView with Column/Wrap; responsive stat tiles (1–3 per row); updated copy Start/Stop Mycelium
• Peers: search + empty state; ellipsis and surfaceVariant progress bars
• settings: dark mode toggle bound to provider; version placeholders
• bugfix: text visibility via onSurface in TextTheme
• misc: margins/overflow fixes and lints clean

#139