add Career W% column from BCP all-events history

For each roster player, fire a parallel fetch to
/placings?placingsType=player&userId={id} and aggregate
wins/losses/ties across all events that have those fields.
Renders asynchronously - shows … while loading, — if no
data found. Column is sortable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

index.html

@@ -75,6 +75,7 @@
               <th class="text-right cursor-pointer select-none" data-sort="pts">ITC Points</th>
               <th class="text-right hidden sm:table-cell cursor-pointer select-none" data-sort="wlt">W–L–T</th>
               <th class="text-right hidden sm:table-cell cursor-pointer select-none" data-sort="wpct">Win %</th>
+              <th class="text-right hidden sm:table-cell cursor-pointer select-none" data-sort="cwpct">Career W%</th>
               <th class="text-right hidden sm:table-cell cursor-pointer select-none" data-sort="rank">ITC Rank</th>
             </tr>
           </thead>