Fix dashboard stat tiles and add sidebar date filters

- Created Today tile: no longer limits to open statuses (count is all statuses)
- Closed Today tile: filters by closed_at range, not updated_at
- Add closed_from/closed_to support to TicketModel and DashboardController
- Add Created/Updated/Closed date range inputs to sidebar filter panel
- Apply button collects date inputs; Clear All removes them
- removeFilter handles date chip removal (clears both _from and _to)
- Active filter chips shown for date ranges

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

models/TicketModel.php

@@ -121,6 +121,18 @@ class TicketModel {
             $paramTypes .= 's';
         }
 
+        // Date range - closed_at
+        if (!empty($filters['closed_from'])) {
+            $whereConditions[] = "DATE(t.closed_at) >= ?";
+            $params[] = $filters['closed_from'];
+            $paramTypes .= 's';
+        }
+        if (!empty($filters['closed_to'])) {
+            $whereConditions[] = "DATE(t.closed_at) <= ?";
+            $params[] = $filters['closed_to'];
+            $paramTypes .= 's';
+        }
+
         // Priority range
         if (!empty($filters['priority_min'])) {
             $whereConditions[] = "t.priority >= ?";