Add date validation for create_conference

src/core/management/commands/create_conference.py

-from argparse import BooleanOptionalAction
+from argparse import ArgumentTypeError, BooleanOptionalAction
 from datetime import datetime
 
 from zoneinfo import ZoneInfo
@@ -331,6 +331,13 @@ def seed_conference(conf: Conference, year: int = 0, force: bool = False):
         )
 
 
+def _validate_date(s: str) -> datetime:
+    try:
+        return datetime.strptime(s, '%Y')  # noqa: DTZ007
+    except ValueError as exc:
+        raise ArgumentTypeError(f"Not a valid date: {s!r}. Use format 'YYYY'") from exc
+
+
 class Command(BaseCommand):
     def add_arguments(self, parser):
         parser.add_argument(
@@ -348,7 +355,7 @@ class Command(BaseCommand):
         parser.add_argument(
             '-y',
             '--year',
-            type=int,
+            type=_validate_date,
             help='The year of the CCC congress. If not given, it will use the current year.',
         )
         parser.add_argument(
@@ -363,9 +370,15 @@ class Command(BaseCommand):
         if not (name := options.get('name')):
             name = input('NAME of the new conference (long title): ')
         if not (year := options.get('year')):
+            year_valid = False
+            while not year_valid:
                 year = input("YEAR of the CCC congress (leave empty if it's something else): ")
-        year = int(year or '0')
-
+                try:
+                    year = datetime.strptime(year, '%Y')  # noqa: DTZ007
+                    year_valid = True
+                except ValueError:
+                    self.stderr.write('Invalid year format. Please use YYYY.')
+        year = year.year
         print(f'Creating conference {slug} ({name}) for year {year}')
 
         # load our bootstrap fixtures