feat: add local-first private AI digest workflow

Migrate app code into canonical feature slices, add phone-only AI digest scheduling and review, wire local notification/background task support, and cover the flow with tests.

lib/core/network/reachability/README.md

@@ -0,0 +1,4 @@
+# Reachability
+
+Network availability checks and platform-specific reachability code live here.
+This folder should answer "can we talk to the network?" and nothing more.

lib/core/network/reachability/network_reachability_io.dart

@@ -30,19 +30,17 @@ class IoNetworkReachability implements NetworkReachability {
   Stream<bool> watch({Duration timeout = const Duration(seconds: 2)}) {
     final Stream<dynamic> changes =
         _connectivity.onConnectivityChanged as Stream<dynamic>;
-    return changes
-        .asyncMap((dynamic event) async {
-          final Iterable<ConnectivityResult> results =
-              _normalizeConnectivityResults(event);
-          final bool hasTransport = results.any(
-            (ConnectivityResult result) => result != ConnectivityResult.none,
-          );
-          if (!hasTransport) {
-            return false;
-          }
-          return isReachable(timeout: timeout);
-        })
-        .distinct();
+    return changes.asyncMap((dynamic event) async {
+      final Iterable<ConnectivityResult> results =
+          _normalizeConnectivityResults(event);
+      final bool hasTransport = results.any(
+        (ConnectivityResult result) => result != ConnectivityResult.none,
+      );
+      if (!hasTransport) {
+        return false;
+      }
+      return isReachable(timeout: timeout);
+    }).distinct();
   }
 
   Iterable<ConnectivityResult> _normalizeConnectivityResults(dynamic event) {