domain: add Media Catalog entities (Asset, Metadata, Stack, Derivative, Duplicate)

crates/domain/tests/entities/asset_metadata.rs

@@ -0,0 +1,17 @@
+use domain::entities::{AssetMetadata, MetadataSource};
+use domain::value_objects::{MetadataValue, StructuredData, SystemId};
+
+#[test]
+fn metadata_source_ordering() {
+    assert!(MetadataSource::ExifExtracted < MetadataSource::AiGenerated);
+    assert!(MetadataSource::AiGenerated < MetadataSource::UserEdited);
+}
+
+#[test]
+fn create_metadata_layer() {
+    let mut data = StructuredData::new();
+    data.insert("camera", MetadataValue::String("Canon".to_string()));
+    let meta = AssetMetadata::new(SystemId::new(), MetadataSource::ExifExtracted, data);
+    assert_eq!(meta.metadata_source, MetadataSource::ExifExtracted);
+    assert_eq!(meta.data.get_string("camera"), Some("Canon"));
+}