Convert the settings window into an independent top-level window with its own taskbar icon and open-or-focus semantics. Removed Owner/anchor/toggle semantics from SettingsWindowService and added ScreenReferenceWindow for centering; settings windows now ShowInTaskbar = true and are truly destroyed on close. Added SettingsWindowPlacementHelper and tests for placement/centering. Main window now respects an AppSettingsSnapshot.ShowInTaskbar flag (new setting exposed in GeneralSettings UI) and slide/visibility animations and "back to Windows" behavior no longer affect the independent settings window. Updated various callers to use OpenIndependentSettingsModule, adjusted window transitions/X offsets, and added/updated spec files documenting the feature and animation boundary.
