Checkpoint: management app redesign, onboarding/signup workflow, and events calendar backend

Large uncommitted body of work accumulated across sessions on this branch --
committing as a checkpoint so it's tracked and future worktree-isolated agents
see the real codebase instead of a stale ancestor commit. Covers the
management app's dedicated Tailwind theme and templates, the club onboarding
requirement/signup workflow (club/services/onboarding.py, requirement/status
models, sign-up dashboard), fee/status auto-activation decoupling, referee
management, and the new events calendar grid service layer.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ECGMEwrc2k4D8VQuwjstj9

teams/models.py

@@ -86,7 +86,16 @@ 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})
+    position = models.ForeignKey(
+        Position,
+        on_delete=models.PROTECT,
+        null=True,
+        blank=True,
+        related_name="team_memberships",
+        verbose_name=_("position"),
+        limit_choices_to={"staff_position": False},
+        help_text=_("Left blank for a member placed on the roster before their position is decided (e.g. from the Sign-up page) -- the team's own manager sets it once known."),
+    )
 
     jersey_number = models.PositiveSmallIntegerField(_("jersey number"), blank=True, null=True)
     is_captain = models.BooleanField(_("is captain"), default=False)