ShellRoute + Home Route

Wires the home route and almost every authenticated screen inside a single ShellRoute whose builder is AppShellScaffold. This is what makes the bottom nav persistent across pushes — secondary screens are children of the shell, not pushes on top of the home screen.

1. GoRouter is constructed in app_router.dart with the redirect we describe in the auth feature.
2. Routes are split: auth/onboarding/splash live OUTSIDE the ShellRoute (no nav bar).
3. Home, settings, cart, prestataires, profile, orders, seller dashboards, etc. live INSIDE the ShellRoute and inherit AppShellScaffold.
4. Some routes (e.g. /map, /messages) are redirect-only GoRoutes that bounce back to /home so the IndexedStack can switch tabs.

• Pushing onto a ShellRoute child preserves the nav bar; pushing the same route name from outside the shell breaks IndexedStack swap.
• The /add-prestation route lives outside the ShellRoute on purpose — it's a full-screen wizard that should NOT show the nav bar.
• /map and /messages exist as redirect-only routes purely to support deep-linking to a specific bottom-nav tab without a custom URL scheme.

• lib/src/core/routing/app_router.dart:332 // ShellRoute builder
• lib/src/core/routing/app_router.dart:338 // home GoRoute
• lib/src/core/routing/app_router.dart:344 // /map redirect
• lib/src/core/routing/app_router.dart:350 // /messages redirect
• lib/src/core/routing/app_router.dart:731 // /add-prestation outside ShellRoute

Adding a new top-level screen? Decide first whether it needs the nav bar — placement (inside vs outside ShellRoute) is the deciding factor.