Add closed tickets checkbox, customer linking for tickets

- Closed tickets completely hidden from default view, separate
  "Suljetut" checkbox to toggle them with search capability
- Removed "Osoitettu" column, added "Asiakas" column to ticket list
- Customer dropdown in ticket detail view to link ticket to a customer
- ticket_customer API endpoint for linking tickets to customers
- ticket_type changelog label added

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

api.php

@@ -1689,6 +1689,35 @@ switch ($action) {
         saveTickets($tickets);
         break;
 
+    case 'ticket_customer':
+        requireAuth();
+        if ($method !== 'POST') break;
+        $input = json_decode(file_get_contents('php://input'), true);
+        $id = $input['id'] ?? '';
+        $customerId = $input['customer_id'] ?? '';
+        $customerName = $input['customer_name'] ?? '';
+        $tickets = loadTickets();
+        $found = false;
+        foreach ($tickets as &$t) {
+            if ($t['id'] === $id) {
+                $t['customer_id'] = $customerId;
+                $t['customer_name'] = $customerName;
+                $t['updated'] = date('Y-m-d H:i:s');
+                $found = true;
+                addLog('ticket_customer', $t['id'], $t['subject'], "Asiakkuus: {$customerName}");
+                echo json_encode($t);
+                break;
+            }
+        }
+        unset($t);
+        if (!$found) {
+            http_response_code(404);
+            echo json_encode(['error' => 'Tikettiä ei löydy']);
+            break;
+        }
+        saveTickets($tickets);
+        break;
+
     case 'ticket_assign':
         requireAuth();
         if ($method !== 'POST') break;