feat(teams): add teams app with roster and staff assignments

Introduce the teams app: Team and Position (both club-scoped, with
per-club unique names), TeamMembership (season-scoped roster with jersey
number + captain flags, unique member and jersey per team/season), and
StaffAssignment (coaching/staff, filtered to staff positions). All
uniqueness expressed as UniqueConstraints.

Register every model in the admin (with roster + staff inlines on Team)
and cover the models with tests. Fix two model bugs surfaced by the
system check: StaffAssignment.position reused TeamMembership's reverse
accessor (Position.team_memberships) and duplicated its constraint name.

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

teams/models.py

@@ -0,0 +1,81 @@
+from django.db import models
+from django.utils.translation import gettext_lazy as _
+
+from club.models import Season
+from clubmanager.base import ClubScopedModel, UUIDModel
+from members.models import Member
+
+
+class Team(ClubScopedModel):
+    name = models.CharField(_("name"), max_length=255)
+    short_name = models.CharField(_("short name"), max_length=255)
+
+    class Meta:
+        verbose_name = _("team")
+        verbose_name_plural = _("teams")
+        constraints = [
+            models.UniqueConstraint(fields=["club", "name"], name="unique_team_name_per_club"),
+        ]
+
+    def __str__(self):
+        return self.name
+
+
+class Position(ClubScopedModel):
+    name = models.CharField(_("name"), max_length=255)
+    short_name = models.CharField(_("short name"), max_length=255)
+    ordering = models.PositiveSmallIntegerField(_("ordering"), default=0)
+
+    staff_position = models.BooleanField(_("staff position"), default=False)
+
+    class Meta:
+        verbose_name = _("position")
+        verbose_name_plural = _("positions")
+        constraints = [
+            models.UniqueConstraint(fields=["club", "name"], name="unique_position_name_per_club"),
+        ]
+        ordering = ["ordering", "name"]
+
+    def __str__(self):
+        return self.name
+
+
+class TeamMembership(UUIDModel):
+    team = models.ForeignKey(Team, on_delete=models.CASCADE, related_name="roster", verbose_name=_("team"))
+    member = models.ForeignKey(Member, on_delete=models.CASCADE, related_name="team_memberships", verbose_name=_("member"))
+    season = models.ForeignKey(Season, on_delete=models.PROTECT, related_name="team_memberships", verbose_name=_("season"))
+    position = models.ForeignKey(Position, on_delete=models.PROTECT, related_name="team_memberships", verbose_name=_("position"), limit_choices_to={"staff_position": False})
+
+    jersey_number = models.PositiveSmallIntegerField(_("jersey number"), blank=True, null=True)
+    is_captain = models.BooleanField(_("is captain"), default=False)
+    is_alternate_captain = models.BooleanField(_("is alternate captain"), default=False)
+
+    class Meta:
+        verbose_name = _("team membership")
+        verbose_name_plural = _("team memberships")
+        ordering = ["team", "member__last_name", "member__first_name"]
+        constraints = [
+            models.UniqueConstraint(fields=["team", "season", "member"], name="unique_member_per_team_per_season"),
+            models.UniqueConstraint(fields=["team", "season", "jersey_number"], name="unique_jersey_number_per_team_per_season"),
+        ]
+
+    def __str__(self):
+        return f"{self.team} - {self.member}"
+
+
+class StaffAssignment(UUIDModel):
+    team = models.ForeignKey(Team, on_delete=models.CASCADE, related_name="staff_assignments", verbose_name=_("team"))
+    member = models.ForeignKey(Member, on_delete=models.CASCADE, related_name="staff_assignments", verbose_name=_("member"))
+    season = models.ForeignKey(Season, on_delete=models.PROTECT, related_name="staff_assignments", verbose_name=_("season"))
+    position = models.ForeignKey(Position, on_delete=models.PROTECT, related_name="staff_assignments", verbose_name=_("position"), limit_choices_to={"staff_position": True})
+
+    class Meta:
+        verbose_name = _("staff assignment")
+        verbose_name_plural = _("staff assignments")
+        ordering = ["team", "member__last_name", "member__first_name"]
+        constraints = [
+            models.UniqueConstraint(fields=["team", "season", "member"], name="unique_staff_member_per_team_per_season"),
+        ]
+
+    def __str__(self):
+        return f"{self.team} - {self.member}"