feat(app): Flutter-клиент — логин, дашборд, потоки, категории, транзакции, правила

Riverpod + go_router с auth-guard, NavigationRail на широком экране и bottom bar
на узком. Токены в flutter_secure_storage, на web access живёт в памяти.
Интерцептор подставляет токен и делает ровно один refresh на 401.

Деньги приходят строками и форматируются через Decimal: парсить их в double
значило бы терять копейки ровно там, где бэкенд их бережёт.

app/.metadata

@@ -0,0 +1,39 @@
+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: "nixpkgs000000000000000000000000000000000"
+  channel: "stable"
+
+project_type: app
+
+# Tracks metadata for the flutter migrate command
+migration:
+  platforms:
+    - platform: root
+      create_revision: nixpkgs000000000000000000000000000000000
+      base_revision: nixpkgs000000000000000000000000000000000
+    - platform: android
+      create_revision: nixpkgs000000000000000000000000000000000
+      base_revision: nixpkgs000000000000000000000000000000000
+    - platform: linux
+      create_revision: nixpkgs000000000000000000000000000000000
+      base_revision: nixpkgs000000000000000000000000000000000
+    - platform: web
+      create_revision: nixpkgs000000000000000000000000000000000
+      base_revision: nixpkgs000000000000000000000000000000000
+    - platform: windows
+      create_revision: nixpkgs000000000000000000000000000000000
+      base_revision: nixpkgs000000000000000000000000000000000
+
+  # User provided section
+
+  # List of Local paths (relative to this file) that should be
+  # ignored by the migrate tool.
+  #
+  # Files that are not part of the templates will be ignored by default.
+  unmanaged_files:
+    - 'lib/main.dart'
+    - 'ios/Runner.xcodeproj/project.pbxproj'