Fix API security: dependency/visibility leaks, authz, CSRF, comment spoofing

- ticket_dependencies.php: pass current user id/groups/is_admin into the
  visibility-filtered DependencyModel methods; drop (int) casts that
  stripped leading zeros from varchar ticket_ids
- update_ticket.php: authorize visibility changes (admin or creator only);
  enforce requires_comment transitions server-side (400 + requires_comment
  flag so the client can prompt-and-retry); return proper 401/400/403
- add_comment.php: take commenter name from the session not the client
  (anti-spoofing); validate parent_comment_id belongs to the ticket;
  reject empty comments; pass ticket visibility to notifications so
  non-public comment bodies aren't leaked
- add_comment/update_comment/bulk_operation: validate CSRF for all
  state-changing methods, not just POST
- bootstrap.php: return the current CSRF token on rejection and never
  rotate it on a rejected request, so a desynced client can auto-recover
- correct auth->401 and validation->400 status codes across these endpoints

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

api/delete_comment.php

@@ -36,7 +36,11 @@ try {
         session_start();
     }
     if (!isset($_SESSION['user']) || !isset($_SESSION['user']['user_id'])) {
-        throw new Exception("Authentication required");
+        ob_end_clean();
+        http_response_code(401);
+        header('Content-Type: application/json');
+        echo json_encode(['success' => false, 'error' => 'Authentication required']);
+        exit;
     }
 
     // CSRF Protection
@@ -64,7 +68,11 @@ try {
         if (isset($_POST['comment_id'])) {
             $data = ['comment_id' => $_POST['comment_id']];
         } else {
-            throw new Exception("Missing required field: comment_id");
+            ob_end_clean();
+            http_response_code(400);
+            header('Content-Type: application/json');
+            echo json_encode(['success' => false, 'error' => 'Missing required field: comment_id']);
+            exit;
         }
     }