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/src/AppLogger.php

@@ -0,0 +1,75 @@
+<?php
+/**
+ * Structured application logger for form submissions.
+ *
+ * Writes JSON-lines to a log file in storage/logs/.
+ * Each entry contains: timestamp, source (admin|partage), action,
+ * status (success|error), context (IP, UA, thesis ID, error message, etc.).
+ */
+class AppLogger
+{
+    private string $logDir;
+    private string $logFile;
+
+    public function __construct(?string $logDir = null)
+    {
+        $this->logDir = $logDir ?? (defined('STORAGE_ROOT') ? STORAGE_ROOT . '/logs' : __DIR__ . '/../storage/logs');
+
+        if (!is_dir($this->logDir)) {
+            mkdir($this->logDir, 0755, true);
+        }
+
+        $this->logFile = $this->logDir . '/form-submissions.log';
+    }
+
+    /**
+     * Log a successful thesis submission.
+     *
+     * @param string  $source   'admin' or 'partage'
+     * @param int     $thesisId
+     * @param string  $identifier  e.g. "2025-003"
+     * @param string  $authorName
+     * @param array   $extras   Additional context (e.g. share link slug)
+     */
+    public function logSubmission(string $source, int $thesisId, string $identifier, string $authorName, array $extras = []): void
+    {
+        $this->write(array_merge([
+            'source'      => $source,
+            'action'      => 'submit',
+            'status'      => 'success',
+            'thesis_id'   => $thesisId,
+            'identifier'  => $identifier,
+            'author'      => $authorName,
+        ], $extras));
+    }
+
+    /**
+     * Log a failed thesis submission.
+     *
+     * @param string    $source
+     * @param string    $errorMessage
+     * @param array     $extras
+     */
+    public function logError(string $source, string $errorMessage, array $extras = []): void
+    {
+        $this->write(array_merge([
+            'source' => $source,
+            'action' => 'submit',
+            'status' => 'error',
+            'error'  => $errorMessage,
+        ], $extras));
+    }
+
+    /**
+     * Write a structured log line.
+     */
+    private function write(array $entry): void
+    {
+        $entry['timestamp'] = date('c');
+        $entry['ip']        = $_SERVER['REMOTE_ADDR'] ?? 'unknown';
+        $entry['user_agent'] = $_SERVER['HTTP_USER_AGENT'] ?? '';
+
+        $line = json_encode($entry, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE) . "\n";
+        error_log($line, 3, $this->logFile);
+    }
+}