feat: Complete Phase 1 Authentication and setup Flutter project structure

- Completed authentication system with signup, login, password reset, and logout
- Enhanced error handling and accessibility across all auth flows
- Added comprehensive loading states and user feedback
- Implemented confirmation dialogs for destructive actions
- Setup complete Flutter project structure with proper configuration
- Added planning documentation for Phase 2 household creation
- All Phase 1 success criteria verified and complete

linux/flutter/generated_plugin_registrant.h

@@ -0,0 +1,15 @@
+//
+//  Generated file. Do not edit.
+//
+
+// clang-format off
+
+#ifndef GENERATED_PLUGIN_REGISTRANT_
+#define GENERATED_PLUGIN_REGISTRANT_
+
+#include <flutter_linux/flutter_linux.h>
+
+// Registers Flutter plugins.
+void fl_register_plugins(FlPluginRegistry* registry);
+
+#endif  // GENERATED_PLUGIN_REGISTRANT_