Add item registry extraction and validation

internal/modules/dnd/extract/itemregistry/model.go

@@ -0,0 +1,15 @@
+package itemregistry
+
+type extractionResponse struct {
+	Items []itemResponse `json:"items"`
+}
+
+type itemResponse struct {
+	Name       string                  `json:"name"`
+	SourceRefs []itemSourceRefResponse `json:"source_refs"`
+}
+
+type itemSourceRefResponse struct {
+	StartUnitID int `json:"start_unit_id"`
+	EndUnitID   int `json:"end_unit_id"`
+}