feat: support smol:// QR sharing, deep links and in-dialog scanning

lib/presentation/app_widget.dart

@@ -1,9 +1,15 @@
+import "dart:async";
+
+import "package:app_links/app_links.dart";
+import "package:auto_route/auto_route.dart";
 import "package:flutter/material.dart";
 import "package:flutter_riverpod/flutter_riverpod.dart";
 
 import "package:smol_mail/data/providers/providers.dart";
-import "package:smol_mail/presentation/theme/theme.dart";
 import "package:smol_mail/presentation/routes/app_router.dart";
+import "package:smol_mail/presentation/routes/app_router.gr.dart";
+import "package:smol_mail/presentation/theme/theme.dart";
+import "package:smol_mail/smol/link.dart";
 
 /// SnackBars need no context through this key, so the client's trust
 /// warnings can be shown from anywhere in the protocol stack.
@@ -17,6 +23,10 @@ class AppWidget extends ConsumerStatefulWidget {
 }
 
 class _AppWidgetState extends ConsumerState<AppWidget> {
+  late final AppRouter _router = AppRouter(ref);
+  final AppLinks _appLinks = AppLinks();
+  StreamSubscription<Uri>? _linkSub;
+
   @override
   void initState() {
     super.initState();
@@ -37,6 +47,33 @@ class _AppWidgetState extends ConsumerState<AppWidget> {
         ),
       );
     };
+
+    _linkSub = _appLinks.uriLinkStream.listen(_handleLink);
+  }
+
+  // A smol:// link is the self-certifying form: the §8 strong path,
+  // confirmed in the import dialog route before its key is bound. The push
+  // waits a frame — the stream can deliver the cold-start link while the
+  // first frame is still being laid out.
+  void _handleLink(Uri uri) {
+    final link = parseSmolLink(uri.toString());
+    if (link == null) return;
+    if (ref.read(identityProvider) == null) {
+      rootScaffoldMessengerKey.currentState?.showSnackBar(
+        const SnackBar(
+            content: Text("finish onboarding before using smol:// links")),
+      );
+      return;
+    }
+    WidgetsBinding.instance.addPostFrameCallback(
+      (_) => _router.push(ImportContactDialogRoute(prefill: link.source)),
+    );
+  }
+
+  @override
+  void dispose() {
+    _linkSub?.cancel();
+    super.dispose();
   }
 
   @override
@@ -48,7 +85,16 @@ class _AppWidgetState extends ConsumerState<AppWidget> {
       themeMode: ThemeMode.system,
       debugShowCheckedModeBanner: false,
       scaffoldMessengerKey: rootScaffoldMessengerKey,
-      routerConfig: AppRouter(ref).config(),
+      // smol:// URIs are for app_links, not the route table. The startup link
+      // must still resolve to a real route — auto_route throws "Can not
+      // resolve initial route" on an unmatched link and leaves a blank
+      // screen — so it lands on the normal entry route, whose guard
+      // redirects to home exactly like a launcher start. Every later
+      // platform link is ignored by the router; the stream handler reacts.
+      routerConfig: _router.config(
+        deepLinkBuilder: (link) =>
+            link.initial ? DeepLink.single(const OnboardingRoute()) : DeepLink.none,
+      ),
     );
   }
 }