refactor(storage): normalize runtime storage roots

[Orinks]

Summary

• resolve a canonical runtime storage layout once at app startup
• route config, runtime state, cache, NOAA prefs, and single-instance lock paths through that layout
• add focused regression coverage for default, portable, and explicit --config-dir storage behavior

Testing

• pytest tests/test_paths.py tests/test_single_instance.py tests/test_runtime_storage_integration.py tests/test_noaa_radio.py tests/test_noaa_radio_dialog.py tests/test_runtime_state_manager.py tests/test_alert_manager.py tests/test_notification_event_manager.py tests/test_split_notification_timers.py tests/test_settings_dialog_portable_copy.py tests/test_config_manager.py -q
• ruff check src/accessiweather/paths.py src/accessiweather/app.py src/accessiweather/app_initialization.py src/accessiweather/config/config_manager.py src/accessiweather/single_instance.py src/accessiweather/noaa_radio/preferences.py src/accessiweather/ui/dialogs/noaa_radio_dialog.py tests/test_paths.py tests/test_single_instance.py tests/test_runtime_storage_integration.py tests/test_noaa_radio.py tests/test_noaa_radio_dialog.py

Closes #471