feat(flutter): project scaffold with pubspec and smoke test

iOS + Android targets only; desktop disabled (per spec, Tauri-wrapped
SvelteKit handles desktop in v1.1). Riverpod + dio + just_audio +
audio_service + go_router pinned in pubspec. Smoke test confirms the
ProviderScope wiring boots a Material app.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/.metadata

@@ -0,0 +1,33 @@
+# 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: "02085feb3f5d8a8156e5e28512b9d99351d510c0"
+  channel: "stable"
+
+project_type: app
+
+# Tracks metadata for the flutter migrate command
+migration:
+  platforms:
+    - platform: root
+      create_revision: 02085feb3f5d8a8156e5e28512b9d99351d510c0
+      base_revision: 02085feb3f5d8a8156e5e28512b9d99351d510c0
+    - platform: android
+      create_revision: 02085feb3f5d8a8156e5e28512b9d99351d510c0
+      base_revision: 02085feb3f5d8a8156e5e28512b9d99351d510c0
+    - platform: ios
+      create_revision: 02085feb3f5d8a8156e5e28512b9d99351d510c0
+      base_revision: 02085feb3f5d8a8156e5e28512b9d99351d510c0
+
+  # 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'