feat(settings): apply a language change without restarting

[howar31]

Cause

Changing the language in Settings > General only took effect after restarting Glimpr. Each engine resolved the choice once at boot, the macOS menu-bar strings were resolved once per launch, and the Windows tray and recording-strip labels were sent once at boot.

Change

• lib/settings/app_locale.dart: loadAppLocaleOverride can be called again and reports whether the language changed. syncNativeLanguage sends the Windows tray and recording-strip labels (moved here from lib/main.dart) and, on macOS, tells the native side to re-read the choice.
• lib/settings/settings_app.dart: picking a language reloads it, rebuilds the window, updates the native strings, and refreshes the tray update label and the What's new sections. The restart hint and button under the language picker are removed, together with the string settingsLanguageAppliesAfterRestart.
• lib/overlay/overlay_app.dart: the overlay engine re-resolves the language after each reveal and after a Settings detour.
• lib/image_editor/image_editor_app.dart: the Image Editor re-resolves the language when its window regains focus or Settings closes.
• macos/Runner/MainFlutterWindow.swift, macos/Runner/StatusItemController.swift: a languageChanged call re-reads the choice, rebuilds the menu-bar menu (keeping the recording state, the recent list and the update label) and re-applies the window titles.
• windows/runner/record_channel.cpp: comment only.
• Tests for the reload, the Windows label push, the macOS call, and the Settings window switching language in place.
• Version 1.25.0+42.

When each surface follows a change: the Settings window and the menu-bar / tray menu right away; the screenshot overlay on the next screenshot; an open Image Editor when its window regains focus; the recording strip on the next recording.

Verification

• flutter analyze and the full flutter test suite pass on macOS and on Windows.
• The macOS native test target passes. flutter build macos --debug and flutter build windows --release succeed.
• Checked on screen in development builds on macOS and Windows: Settings window, menu-bar / tray menu, screenshot overlay, Image Editor, recording strip.