Add Team/TeamRole/TeamMembership/TeamPicture models and fix two test bugs

- Fix Member.create(): post_save signal creates Member immediately on User creation,
  so new users always hit the hasattr branch; check `created` flag to set initial
  password and notes for genuinely new users
- Fix Season.for_date(): replace get() with filter().order_by("-start_date").first()
  to handle overlapping seasons gracefully and raise DoesNotExist when none match
- Add TeamRole, Team, TeamMembership, TeamPicture models with rules permissions
- Add migration 0002 for new models
- Add test suites for members and teams covering all new model behaviour

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

members/models.py

@@ -83,7 +83,13 @@ class Member(RulesModel):
 
             if hasattr(user, "member"):
                 member = user.member
-                if password is not None and password != "":
+                if created:
+                    if password is None or password == "":
+                        initial_password = "".join(secrets.choice(string.ascii_letters + string.digits) for _ in range(20))
+                        password = initial_password
+                        member.notes = f"Initial password: {initial_password}"
+                    user.set_password(password)
+                elif password is not None and password != "":
                     user.set_password(password)
             else:
                 member = cls()