fix: Add missing QCheckBox import and fix Qt.QSize reference

1. Added QCheckBox to perfect_ux.py imports (was missing)
2. Fixed dashboard_view.py: Qt.QSize -> QSize (QtCore import)

These fix the NameError and AttributeError that prevented the app from starting.

core/perfect_ux.py

@@ -28,7 +28,7 @@ from PyQt6.QtWidgets import (
     QStackedWidget, QLabel, QPushButton, QFrame,
     QScrollArea, QGridLayout, QSizePolicy, QSpacerItem,
     QGraphicsDropShadowEffect, QProgressBar, QToolTip,
-    QDialog, QLineEdit, QTextEdit
+    QDialog, QLineEdit, QTextEdit, QCheckBox
 )
 from PyQt6.QtCore import (
     Qt, QTimer, pyqtSignal, QSize, QPropertyAnimation,

core/ui/dashboard_view.py

@@ -8,7 +8,7 @@ from PyQt6.QtWidgets import (
     QWidget, QVBoxLayout, QHBoxLayout, QLabel,
     QGridLayout, QFrame, QScrollArea, QPushButton
 )
-from PyQt6.QtCore import Qt
+from PyQt6.QtCore import Qt, QSize
 
 from core.icon_manager import get_icon_manager
 
@@ -89,7 +89,7 @@ class DashboardView(QWidget):
         # Plugin store button with icon
         store_btn = QPushButton("Open Plugin Store")
         store_btn.setIcon(self.icon_manager.get_icon("shopping-bag"))
-        store_btn.setIconSize(Qt.QSize(18, 18))
+        store_btn.setIconSize(QSize(18, 18))
         store_btn.setStyleSheet("""
             QPushButton {
                 background-color: #ff8c42;