feat(alerts): add opt-in immediate alert popups

[Orinks]

Summary

• add an opt-in setting for immediate alert detail popups while AccessiWeather is already running
• reuse AlertManager eligibility/filtering so single eligible alerts open the existing detail dialog and multi-alert batches open one combined dialog
• keep the main window hidden/minimized when showing these popups and cover the new behavior with targeted tests

Verification

• pytest -q tests/test_models.py tests/test_settings_dialog_tray_text.py tests/test_alert_notification_system.py tests/test_app_immediate_alert_popups.py tests/test_app_notification_activation.py tests/test_system_tray.py tests/gui/test_main_window_minimize.py
• ruff check src/accessiweather/app.py src/accessiweather/alert_notification_system.py src/accessiweather/app_initialization.py src/accessiweather/models/config.py src/accessiweather/ui/dialogs/alerts_summary_dialog.py src/accessiweather/ui/dialogs/init.py src/accessiweather/ui/dialogs/settings_tabs/notifications.py tests/test_alert_notification_system.py tests/test_app_immediate_alert_popups.py tests/test_models.py tests/test_settings_dialog_tray_text.py

Notes

• local pyright/Claude/Gemini CLI review was not available in this environment