Add referee assignment/eligibility system, team bulk-add, member Groups, and referee management dashboard with PDF export

Builds the referee workflow end to end: club-defined RefereeLevel/RefereeProfile
eligibility tied to teams, EventReferee assignment (member or external, with
fee/km payment tracking), an admin dashboard with KPI tiles, date-grouped game
tiles and range filters, and a downloadable payment form PDF modeled on the
club's existing paper document (using Club.legal_name when set). Also lands
team roster bulk-add, member mass-upload with family linking, and the
members.Group model, developed alongside this work.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

billing/templates/billing/invoice.html

@@ -52,7 +52,7 @@
         <div class="parties">
             <div>
                 <h2>Billed to</h2>
-                <div><strong>{{ club.name }}</strong></div>
+                <div><strong>{{ club.official_name }}</strong></div>
                 <div class="muted">{{ club.slug }}.rosterchief.app</div>
             </div>
             <div class="right">