Show restart notification when restart-required settings change

[mrtineuAI]

Fixes #662.

Some settings only take effect after an application restart (currently the local Autogram API server toggle — the trusted-countries list already refreshes live on save). Users often missed the small hint next to the setting and were confused when the change didn't seem to apply.

This change notifies the user upon saving: after clicking "Save settings", if any restart-required setting was changed since the last save, a modal dialog appears asking them to restart the application. The same notification is shown after confirming a settings reset, when the reset flips such a setting.

Changes:

• UserSettings.restartRequiredSettingsChanged() / restartRequiredSettingsChangedByReset() — detect the change (same prefs-comparison pattern as the existing tlCountriesChanged())
• New modal settings-restart-dialog.fxml + SettingsRestartDialogController, shown from SettingsDialogController.onSaveButtonAction and SettingsResetDialogController.onConfirmResetButtonAction
• New settings.restart.title / settings.restart.text strings in SK and EN bundles
• 2 new unit tests in UserSettingsTest

Verified:

• Scripted GUI click-throughs (real app under xvfb, real mouse clicks): before the fix, toggling the server setting and saving showed no notification (issue replicated); after the fix the "Application restart required" dialog appears and closes via its button; saving with no changes shows nothing; the reset flow also notifies; Slovak localization renders correctly.
• Unit tests: 10/10 pass (UserSettingsTest, incl. the 2 new tests).

[mrtineuAI]

Demo video of the fix in action (scripted click-through of the real app):

https://github.com/mrtineuAI/autogram/releases/download/demo-662/autogram-662-demo.mp4

The video shows: opening Settings, switching to the Other tab, toggling "Enable Autogram API" (a setting that requires an application restart), clicking "Save settings" — and the new "Application restart required" dialog appearing.

[mrtineuAI]

Update: the dialog now has a Restart button (primary) next to Close. Clicking it relaunches Autogram on the spot — same JVM arguments, classpath and program arguments — and exits the old instance.

Demo (scripted click-through of the real app):

autogram-662-restart-demo.mp4

The video shows: toggling "Enable Autogram API" → Save → the dialog with Restart/Close → clicking Restart → the app closing and starting again. (The "Failed to start server" notice at the end is specific to the demo machine, where another Autogram instance already occupies the API port — it also confirms the restarted app picked up the changed setting.)