Gets the appropriate Font Awesome icon class for an artifact.
The artifact to get an icon for (MJConversationArtifactEntity or MJArtifactEntity)
OptionalpluginIcon: stringOptional icon provided by a viewer plugin (highest priority)
Font Awesome icon class (e.g., 'fa-file-code', 'fa-chart-line')
Service for determining which icon to display for artifacts. Implements a three-tier fallback strategy: