feat: initialize Flutter project with version management

- Initialize Flutter 3.38 project with all platforms
- Add build-time version generation from pubspec.yaml
- Print version to console on app startup
- Create CHANGELOG.md following Keep a Changelog format
- Update .gitignore for Flutter + generated files
- Basic app scaffold with Material 3 theming

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

linux/runner/my_application.h

@@ -0,0 +1,21 @@
+#ifndef FLUTTER_MY_APPLICATION_H_
+#define FLUTTER_MY_APPLICATION_H_
+
+#include <gtk/gtk.h>
+
+G_DECLARE_FINAL_TYPE(MyApplication,
+                     my_application,
+                     MY,
+                     APPLICATION,
+                     GtkApplication)
+
+/**
+ * my_application_new:
+ *
+ * Creates a new Flutter-based application.
+ *
+ * Returns: a new #MyApplication.
+ */
+MyApplication* my_application_new();
+
+#endif  // FLUTTER_MY_APPLICATION_H_