Unit tests for QML Dialogs and Feedback components #359

Part of #356

Add unit tests in tests/qml/ for modal dialogs and feedback components:

• SaveDiscardDialog.qml (save, discard, and cancel signals)
• TimePickerPopup.qml (time selection and confirmation)
• ColorPicker.qml (palette pick, custom color value)
• AccountSelectorDialog.qml (account list pick and switch signal)
• ContentPickerDialog.qml (single and multi selection behavior)
• NotificationBell.qml (unread counter badge and click)
• NotificationPopup.qml (popup message, dismiss, timeout)
• LoadingIndicator.qml (running state and visibility)
• LoadMoreFooter.qml (list bottom loading state and retry trigger)

Note: CreateUpdateDialog.qml is deprecated and tracked for cleanup in #367.