feat: dual upload system — direct file storage + PeerTube API integration

Adds a parallel PeerTube upload system behind a feature flag (disabled by default
until upload quota is granted). When disabled, the existing direct file upload
path works unchanged.

Files:
- src/PeerTubeService.php — credential storage (encrypted), OAuth2 token
  retrieval, multipart upload to /api/v1/videos/upload
- migrations/021_peertube_settings.sql — peertube_settings singleton table
  + peertube_upload_enabled site_setting (default 0)
- admin/actions/settings.php — peertube section handler
- admin/parametres.php / templates/admin/parametres.php — PeerTube UI section
- partage/fichiers-fragment.php — shows file inputs when enabled, TODO notice otherwise
- ThesisCreateController / ThesisEditController — handlePeerTubeUpload()
- tfe.php — PeerTube iframe embed detection
- AdminLogger — logPeerTubeUpdate()

app/public/admin/actions/settings.php

@@ -12,6 +12,7 @@ if (!isset($_POST['csrf_token'], $_SESSION['csrf_token'])
 
 require_once APP_ROOT . '/src/Database.php';
 require_once APP_ROOT . '/src/SmtpRelay.php';
+require_once APP_ROOT . '/src/PeerTubeService.php';
 require_once APP_ROOT . '/src/AdminLogger.php';
 $db     = new Database();
 $logger = AdminLogger::make();
@@ -70,6 +71,25 @@ if ($section === 'formulaire') {
             $_SESSION['_flash_smtp_field'] = $test['field'];
         }
     }
+} elseif ($section === 'peertube') {
+    // Feature flag
+    $enabled = isset($_POST['peertube_upload_enabled']) ? '1' : '0';
+    $db->setSetting('peertube_upload_enabled', $enabled);
+
+    // Credentials — only overwrite password when user typed something
+    $data = [
+        'instance_url' => $_POST['peertube_instance_url'] ?? '',
+        'username'     => $_POST['peertube_username']     ?? '',
+        'channel_id'   => $_POST['peertube_channel_id']  ?? 1,
+        'privacy'      => $_POST['peertube_privacy']      ?? 1,
+    ];
+    $pwd = $_POST['peertube_password'] ?? '';
+    if ($pwd !== '') {
+        $data['password'] = $pwd;
+    }
+    PeerTubeService::updateSettings($db, $data);
+    $logger->logPeerTubeUpdate($enabled === '1');
+    App::flash('success', 'Paramètres PeerTube mis à jour.');
 } else {
     App::flash('error', "Section inconnue.");
 }