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/partage/index.php

@@ -500,11 +500,20 @@ function handleShareLinkSubmission(string $slug): void
 
     require_once APP_ROOT . '/src/Controllers/ThesisCreateController.php';
     require_once APP_ROOT . '/src/StudentEmail.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('partage', $thesisId, $identifier, $authorName, [
+            'share_slug' => $slug,
+        ]);
+
         // Send confirmation e-mail (non-blocking; failure doesn't stop redirect)
         $emailSent = StudentEmail::sendConfirmation(Database::getInstance(), $thesisId, $_POST);
 
@@ -521,6 +530,12 @@ function handleShareLinkSubmission(string $slug): void
         header('Location: /partage/thanks?id=' . urlencode((string)$thesisId));
         exit();
     } catch (Exception $e) {
+        $logger->logError('partage', $e->getMessage(), [
+            'share_slug' => $slug,
+            'author'     => $authorName,
+            'post_keys'  => array_keys($_POST),
+        ]);
+
         error_log('Share link submission error: ' . $e->getMessage());
 
         $_SESSION['_flash_error'] = $e->getMessage();