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.

ios/Podfile

@@ -1,5 +1,5 @@
 # Uncomment this line to define a global platform for your project
-# platform :ios, '13.0'
+platform :ios, '14.0'
 
 # CocoaPods analytics sends network stats synchronously affecting flutter build latency.
 ENV['COCOAPODS_DISABLE_STATS'] = 'true'
@@ -29,8 +29,12 @@ flutter_ios_podfile_setup
 
 target 'Runner' do
   use_frameworks!
+  use_modular_headers!
 
   flutter_install_all_ios_pods File.dirname(File.realpath(__FILE__))
+  target 'Share Extension' do
+    inherit! :search_paths
+  end
   target 'RunnerTests' do
     inherit! :search_paths
   end