fix: Add table alias to COUNT query for advanced filters

The WHERE conditions use 't.' prefix but the COUNT query was missing
the table alias, causing 500 errors when using priority_max, assigned_to,
or date filters.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

models/TicketModel.php

@@ -172,7 +172,7 @@ class TicketModel {
         $sortDirection = strtolower($sortDirection) === 'asc' ? 'ASC' : 'DESC';
 
         // Get total count for pagination
-        $countSql = "SELECT COUNT(*) as total FROM tickets $whereClause";
+        $countSql = "SELECT COUNT(*) as total FROM tickets t $whereClause";
         $countStmt = $this->conn->prepare($countSql);
 
         if (!empty($params)) {