Move IResourceNodeFactory to ILSpyX.Abstractions and GuessFileType to ILSpyX.Util
so both UIs can consume them. Wire ResourceEntryNode.Create(Resource) to walk the
MEF-discovered IResourceNodeFactory list (falls back to the generic node), make
Avalonia's ILSpyTreeNode implement ITreeNode for that contract, and register a
ResourcesFileTreeNodeFactory to keep .resources files routed correctly. Adds the
Save virtual on ILSpyTreeNode plus inline "Save" buttons + SaveAsync on
ResourceEntryNode/ResourceTreeNode using a new FilePickers helper around
StorageProvider.SaveFilePickerAsync.
Assisted-by: Claude:claude-opus-4-7:Claude Code