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

ARCHITECTURE.md

@@ -409,7 +409,7 @@ ClubMembership(ClubScopedModel)      # -> carries `club`
   status       CharField (TextChoices: pending | active | lapsed | cancelled)
   fee_status   CharField (TextChoices: unpaid | partial | paid | waived)
   signed_up_at DateTimeField (null)     # when the member registered for the season
-  activated_at DateTimeField (null)     # when membership became active (usually on payment)
+  activated_at DateTimeField (null)     # when membership became active (admin approval only, never on payment alone)
   Meta: unique_together (club, member, season); ordering = ["-season__start_date", ...]
 ```