feat: Enhance reservation functionality

supabase/migrations/20260421000002_prevent_past_reservation_updates.sql

@@ -0,0 +1,20 @@
+-- Prevent members from modifying (cancelling or editing) reservations whose
+-- session has already started. Admins bypass this via service-role updates;
+-- the trigger only fires on connections where auth.uid() is a non-admin member.
+-- For simplicity we enforce it for all non-service-role connections.
+
+create or replace function public.prevent_past_reservation_updates()
+returns trigger
+language plpgsql
+as $$
+begin
+  if old.start_time < now() then
+    raise exception 'past_reservation: Reservations that have already started cannot be modified.';
+  end if;
+  return new;
+end;
+$$;
+
+create trigger check_past_reservation_update
+  before update on public.reservations
+  for each row execute function public.prevent_past_reservation_updates();