Add LaunchBox clear logo provider to Extra Metadata Loader

[mjd4219]

Summary

• Adds LaunchBox as an additional clear-logo source for Extra Metadata Loader.
• Uses LaunchBox Metadata.zip to build a local clear-logo cache and downloads images through the LaunchBox image CDN.
• Adds a manual LaunchBox logo download menu item and an opt-in automatic/library-update setting.

Validation

• Built source/Generic/ExtraMetadataLoader/ExtraMetadataLoader.sln Release with 0 warnings and 0 errors.
• Manually tested the packaged extension in Playnite 10.55: LaunchBox logo download completes and downloads logos successfully.
• Fixed DI constructor visibility discovered during manual testing.
• Fixed LaunchBox XML parsing and bumped the cache schema so an empty cache rebuilds automatically.

[mjd4219]

A packaged .pext for manual testing is available on my fork release: https://github.com/mjd4219/PlayniteExtensionsCollection/releases/tag/launchbox-clear-logo-test-1