add structured logging for admin/partage form submissions + migration system

- AppLogger: JSON-line logger in storage/logs/form-submissions.log
- Logs submissions (admin + partage) with IP, UA, thesis ID, author
- Logs errors with context (post keys, share slug)
- Migration runner (app/migrations/run.php) handles schema drift
- 001_add_objet_column.sql fixes production DB missing 'objet' column
- ThesisCreateController::getIdentifier() helper for logging

app/public/admin/actions/formulaire.php

@@ -19,17 +19,29 @@ if (!isset($_POST['csrf_token'], $_SESSION['csrf_token'])
 error_log('FILES array: ' . print_r($_FILES, true));
 
 require_once APP_ROOT . '/src/Controllers/ThesisCreateController.php';
+require_once APP_ROOT . '/src/AppLogger.php';
+
+$logger     = new AppLogger();
+$authorName = $_POST['auteurice'] ?? 'unknown';
 
 try {
     $ctrl     = ThesisCreateController::make();
     $thesisId = $ctrl->submit($_POST, $_FILES);
 
+    $identifier = $ctrl->getIdentifier($thesisId);
+    $logger->logSubmission('admin', $thesisId, $identifier, $authorName);
+
     unset($_SESSION['csrf_token']);
 
     header('Location: ' . $redirect);
     exit();
 
 } catch (Exception $e) {
+    $logger->logError('admin', $e->getMessage(), [
+        'author'   => $authorName,
+        'post_keys' => array_keys($_POST),
+    ]);
+
     error_log('ThesisCreateController error: ' . $e->getMessage());
 
     App::flash('error', $e->getMessage());