fix: TFE and annexes files not saved, plus keyword validation and file preview CSS

- ThesisCreateController::submit() was missing call to handleAnnexeFiles
- ThesisEditController::save() was missing annexe upload handling
- handleAnnexeFiles now applies ALLOWED_MIME_TYPES/ALLOWED_EXTENSIONS validation
  (same restrictions as TFE files, formerly only size was checked)
- Use correct $_FILES key 'annexes' (matching the form input name)
- Relax keyword minimum: admin create/edit require 1+, student (partage) requires 3
- Add CSS styles for file preview items (.fp-item, .fp-thumb, .fp-icon,
  .fp-meta, .fp-name, .fp-size) so multi-file previews (annexes, etc.) wrap correctly
- Fix TFE file input accept attribute in fichiers-fragment.php to include
  video/audio/archive extensions

app/src/Controllers/ThesisEditController.php

@@ -294,8 +294,8 @@ class ThesisEditController
             $keywords = array_values(array_unique($keywords));
             $keywords = array_filter($keywords, fn($t) => $t !== '');
             $keywords = array_slice($keywords, 0, 10);
-            if (count($keywords) < 3) {
-                throw new Exception('Veuillez indiquer au moins 3 mots-clés.');
+            if (count($keywords) < 1) {
+                throw new Exception('Veuillez indiquer au moins 1 mot-clé.');
             }
             $this->db->setThesisTags($thesisId, $keywords);
             error_log('[ThesisEdit] Step 6 OK — tags=' . json_encode($keywords));
@@ -425,6 +425,11 @@ class ThesisEditController
             $this->handleTfeFiles($thesisId, $files['files'], $folderPath, $filePrefix, $post, $tfeCount + 1);
         }
 
+        // ── New annexe files upload ────────────────────────────────────────────
+        if (isset($files['annexes']) && is_array($files['annexes']['name'] ?? null)) {
+            $this->handleAnnexeFiles($thesisId, $files['annexes'], $folderPath, $filePrefix, $post);
+        }
+
         // ── PeerTube video / audio uploads ────────────────────────────────────
         $this->handlePeerTubeUpload($thesisId, trim($post['titre'] ?? ''), $files, 'peertube_video');
         $this->handlePeerTubeUpload($thesisId, trim($post['titre'] ?? ''), $files, 'peertube_audio');