gui: narrow saves checkbox column + app window icon

- Saves checkbox column fixed at 28px.
- Add a PlayStation-style app icon (img/app-icon.png) and set it as the
  window icon on launch.

app/gui.py

@@ -3376,6 +3376,8 @@ class SavesPage(QWidget):
 
         self.table = QTableWidget(0, 6)
         self.table.setHorizontalHeaderLabels(["", "Save", "ID", "PSP", "PPSSPP", "Cloud"])
+        self.table.horizontalHeader().setSectionResizeMode(0, QHeaderView.Fixed)
+        self.table.setColumnWidth(0, 28)
         self.table.horizontalHeader().setSectionResizeMode(1, QHeaderView.Stretch)
         self.table.verticalHeader().setVisible(False)
         self.table.setEditTriggers(QAbstractItemView.NoEditTriggers)
@@ -5061,6 +5063,9 @@ def main():
     init_db()  # migrate legacy on-share DB/covers to local storage, then schema
     log.info("starting psp-preserve (db: %s)", config.DB_PATH)
     app = QApplication(sys.argv)
+    icon_path = config.PROJECT_ROOT / "img" / "app-icon.png"
+    if icon_path.is_file():
+        app.setWindowIcon(QIcon(str(icon_path)))
     window = MainWindow()
     window.show()
     log.info("main window ready")