feat: Add main application window with tabbed interface and bump version to 5.4.0.

gui/main_window.py

@@ -164,7 +164,7 @@ class MainWindow:
         
         # Training Sim Tab
         self.sim_frame = TrainingSimFrame(self.notebook)
-        self.notebook.add(self.sim_frame, text="  📈 Training Sim  ")
+        self.notebook.add(self.sim_frame, text="  📈 Training Sim (Beta)  ")
     
     def create_status_bar(self, parent):
         """Create status bar at bottom"""

version.py

@@ -4,7 +4,7 @@ This file is the single source of truth for the application version.
 """
 
 # Semantic versioning: MAJOR.MINOR.PATCH
-VERSION = "5.3.2"
+VERSION = "5.4.0"
 
 # Application metadata
 APP_NAME = "UmamusumeCardManager"