Code Quality: Improved startup performance

[hez2010]

Related #4180

• Required navigation controls are created before the first layout.
• Hidden Listary controls run after initial rendering.
• Localization reuses a resource context and resets caches on language changes.
• Icon-path calculation is lazy and uses InstalledPath.
• Quick Access enumeration, metadata, and icon extraction run on worker STA threads.
• Reading missing settings no longer immediately writes defaults to disk.
• Prepare the window backdrop before page construction