Show trip country list in order visited

agenda/types.py

@@ -55,17 +55,21 @@ class Trip:
         return max_date if max_date != date.min else None
 
     @property
-    def countries(self) -> set[Country]:
-        """Trip countries."""
-        found: set[Country] = set()
+    def countries(self) -> list[Country]:
+        """Countries visited as part of trip, in order."""
+        seen: set[str] = set()
+        items: list[Country] = []
         for item in self.conferences + self.accommodation:
             if "country" not in item:
                 continue
+            if item["country"] in seen:
+                continue
+            seen.add(item["country"])
             country = agenda.get_country(item["country"])
             assert country
-            found.add(country)
+            items.append(country)
 
-        return found
+        return items
 
     @property
     def countries_str(self) -> str: