Complete people-domain move into members app; keep names on Member

Finish relocating Member/Family/FamilyMembership from authentication into
a dedicated members app, and revert the half-applied move of member names
onto the global User.

- members: add first_name/last_name back to Member (the whole codebase —
  tests, CSV importer, club app, admin — assumes them, and login-less
  children in families need a name); restore local ordering/index and the
  member__last_name lookups in Family.__str__ and FamilyMembership.
- authentication: drop first_name/last_name from User; get_full_name/
  get_short_name delegate to the linked member, else fall back to email.
- migrations: create members.0001_initial, repoint club.ClubMembership FK
  (club.0005), delete the models from authentication (0004, rewritten to
  plain DeleteModel ops in child-first order to avoid a SQLite table-remake
  crash).
- fix stale imports across apps (authentication/club tests, CSV importer)
  and missing imports/URLs in members tests; add missing _ import in
  members/admin.py; export MemberCsvImporter from members.services.

Full suite green (64 tests), ruff clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

members/management/commands/import_members_csv.py

@@ -0,0 +1,43 @@
+from django.core.management.base import BaseCommand, CommandError
+
+from members.services import MemberCsvImporter
+
+
+class Command(BaseCommand):
+    help = "Import club members from a CSV file."
+
+    def add_arguments(self, parser) -> None:
+        parser.add_argument(
+            "csv_file",
+            type=str,
+            help="Path to the CSV file to import.",
+        )
+        parser.add_argument(
+            "--date-format",
+            default="%Y-%m-%d",
+            help="Date format for date_of_birth. Default: %%Y-%%m-%%d",
+        )
+
+    def handle(self, *args, **options) -> str | None:
+        importer = MemberCsvImporter(date_format=options["date_format"])
+
+        try:
+            result = importer.import_path(options["csv_file"])
+        except Exception as exc:
+            raise CommandError(str(exc)) from exc
+
+        for error in result.errors:
+            self.stderr.write(self.style.ERROR(f"Row {error.row_number} skipped: {error.message}"))
+
+        self.stdout.write(
+            self.style.SUCCESS(
+                "Import complete. "
+                f"Members created: {result.created_members}. "
+                f"Members updated: {result.updated_members}. "
+                f"Users created: {result.created_users}. "
+                f"Clubs created: {result.created_clubs}. "
+                f"Memberships created: {result.created_memberships}. "
+                f"Memberships updated: {result.updated_memberships}. "
+                f"Rows skipped: {result.skipped_rows}."
+            )
+        )