Harden recurring cron, bulk delete, error handling; fix semgrep CI

Continued fixes from the multi-agent review:

- recurring tickets cron: now that the parse error is fixed the job runs,
  exposing two latent bugs. (1) next_run_at was only advanced after the
  full success path, so any failure (e.g. a NULL created_by passed to the
  non-nullable assignTicket() $assignedBy -> TypeError) left it in the past
  and re-created a duplicate ticket every cron cycle. Added an atomic
  claimForRun() (conditional UPDATE gated on still-due) called BEFORE
  creation, which also prevents overlapping runs from double-creating.
  (2) The cron used a raw mysqli with no utf8mb4, corrupting non-ASCII
  content; it now uses Database::getConnection(). Also guard the assignment
  so created_by NULL falls back to the assignee.
- bulk delete: attachment files were unlinked inside the DB transaction, so
  an atomic-mode rollback restored rows but the files were already gone.
  deleteTicket() can now defer file removal to the caller, and
  BulkOperationsModel deletes files only after a successful commit.
- UserModel: back-tick the `groups` column (reserved word on MySQL 8.0.2+).
- create_ticket_api.php: stop leaking raw DB/exception messages to callers;
  log server-side and return a generic error. (Also includes a pre-existing
  working-tree tweak that adds title to the manual-ticket dedupe hash.)
- CI: semgrep install failed under PEP 668; add --break-system-packages.

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

create_ticket_api.php

@@ -45,9 +45,11 @@ $conn = new mysqli(
 );
 
 if ($conn->connect_error) {
+    error_log('create_ticket_api: DB connection failed: ' . $conn->connect_error);
+    http_response_code(500);
     echo json_encode([
         'success' => false,
-        'error' => 'Database connection failed: ' . $conn->connect_error
+        'error' => 'Internal server error'
     ]);
     exit;
 }
@@ -199,6 +201,11 @@ function generateTicketHash($data)
         )),
     ];
 
+    // Manual tickets should be unique by title (so different software installs don't collide)
+    if ($sourceType === 'manual') {
+        $stableComponents['title'] = $title;
+    }
+
     // Include hostname for node-specific issues
     if (!$isClusterWide) {
         $stableComponents['hostname'] = $hostname;
@@ -397,7 +404,9 @@ try {
         // Race condition: another node inserted the same hash between our SELECT and INSERT
         echo json_encode(['success' => false, 'error' => 'Duplicate ticket']);
     } else {
-        echo json_encode(['success' => false, 'error' => $e->getMessage()]);
+        error_log('create_ticket_api: insert failed: ' . $e->getMessage());
+        http_response_code(500);
+        echo json_encode(['success' => false, 'error' => 'Internal server error']);
     }
     exit;
 }