feat: tag derivation from ClaML metadata + validity

src/tags.rs

@@ -1 +1,12 @@
-// implemented in a later task
+use crate::model::{IcdMeta, Tags};
+
+/// Build display/filter Tags from ICD metadata and the Alpha-ID
+/// validity flag of the matched entry.
+pub fn tags_for(m: &IcdMeta, alpha_valid: bool) -> Tags {
+    Tags {
+        billable: m.para295 == "P",
+        valid: alpha_valid,
+        chapter: m.chapter.clone(),
+        exotic: m.exotic,
+    }
+}