Add GitHub release update checks

[rimtty]

Summary

• add manual update checks to the notification-area menu and QuickPods Settings
• add an opt-in startup check with a 24-hour throttle and cached result metadata
• query the official GitHub latest stable Release endpoint without downloading or executing packages
• add English and Japanese UI, notifications, documentation, privacy notes, and localization parity coverage
• tune the Settings window for 175% DPI without introducing a scrollbar

User impact

Users can check whether a newer QuickPods Release exists and open the validated official Release page. Automatic checks remain disabled by default and, when enabled, run at most once every 24 hours.

Validation

• dotnet format QuickPods.sln --no-restore --verify-no-changes --severity warn --verbosity minimal
• dotnet build QuickPods.sln -c Release --no-restore — 0 warnings, 0 errors
• dotnet test tests/QuickPods.Foundation.Tests/QuickPods.Foundation.Tests.csproj -c Release — 146 passed
• portable payload validation and root QuickPods.exe launch passed
• manual GitHub Release check and Japanese UI verified at 175% DPI

Known environment-sensitive test

The full solution run still reports the pre-existing Rapid_click_to_jump_updates_present_expected_frames_without_GDI_growth USER-handle assertion on this desktop environment. All other test projects pass; the failure is unrelated to the update-check implementation.