Add EmuMovies video provider to Extra Metadata Loader

[mjd4219]

Summary

• Adds EmuMovies as a full video trailer provider for Extra Metadata Loader.
• Supports encrypted EmuMovies credential storage, credential testing, selectable video quality, and optional HD/HQ/SQ fallback.
• Adds an EmuMovies video download context-menu action with automatic or manual match selection.
• Discovers EmuMovies FTP platform directories dynamically and retries transient directory listing failures.
• Adds only the new English localization strings in en_US.xaml, matching existing upstream localization guidance.

Validation

• Built source/Generic/ExtraMetadataLoader/ExtraMetadataLoader.sln in Release.
• Packaged with Playnite Toolbox.
• Manually tested EmuMovies login, credential test/save, settings UI, single-game video downloads, multi-game video downloads, automatic selection, manual chooser selection, and HD/HQ/SQ fallback.