feat: Add hotkey (Ctrl+Shift+B) to toggle Activity Bar

- Added Ctrl+Shift+B hotkey to toggle activity bar visibility
- Added _on_activity_bar_hotkey() handler method
- Updated startup messages to show all hotkeys including activity bar

Hotkeys:
- Ctrl+Shift+U: Toggle main overlay
- Ctrl+Shift+H: Hide all overlays
- Ctrl+Shift+B: Toggle activity bar

core/main.py

@@ -145,6 +145,7 @@ class EUUtilityApp:
         print("EU-Utility started!")
         print("Press Ctrl+Shift+U to toggle overlay")
         print("Press Ctrl+Shift+H to hide all overlays")
+        print("Press Ctrl+Shift+B to toggle activity bar")
         print("Or double-click the floating icon")
         print(f"Loaded {len(self.plugin_manager.get_all_plugins())} plugins")
         
@@ -295,6 +296,8 @@ class EUUtilityApp:
                 keyboard.add_hotkey('ctrl+shift+u', self._on_hotkey_pressed)
                 # Hide all overlays
                 keyboard.add_hotkey('ctrl+shift+h', self._on_hide_overlays_pressed)
+                # Toggle activity bar
+                keyboard.add_hotkey('ctrl+shift+b', self._on_activity_bar_hotkey)
             except Exception as e:
                 print(f"Failed to register hotkey: {e}")
     
@@ -308,6 +311,14 @@ class EUUtilityApp:
         if self.overlay_manager:
             self.overlay_manager.hide_all()
     
+    def _on_activity_bar_hotkey(self):
+        """Called when activity bar hotkey is pressed."""
+        if self.activity_bar:
+            if self.activity_bar.isVisible():
+                self.activity_bar.hide()
+            else:
+                self.activity_bar.show()
+    
     def _on_toggle_signal(self):
         """Handle toggle signal in main thread."""
         self._toggle_overlay()