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/ThesisCreateController.php

@@ -197,6 +197,7 @@ class ThesisCreateController
         $this->handleCoverUpload($thesisId, $files['couverture'] ?? null, $folderPath, $filePrefix);
         $this->handleNoteIntentionUpload($thesisId, $files['note_intention'] ?? null, $folderPath, $filePrefix);
         $nextNum = $this->handleTfeFiles($thesisId, $files['files'] ?? null, $folderPath, $filePrefix, $post, 1);
+        $this->handleAnnexeFiles($thesisId, $files['annexes'] ?? null, $folderPath, $filePrefix, $post);
         // PeerTube file rows don't go on disk, but the uploads themselves are processed separately
 
         // ── 5b. PeerTube video / audio uploads ────────────────────────────────
@@ -429,7 +430,7 @@ class ThesisCreateController
         if (count($keywords) > 10) {
             throw new Exception('Maximum 10 mots-clés autorisés.');
         }
-        if (count($keywords) < 3) {
+        if (!$adminMode && count($keywords) < 3) {
             throw new Exception('Veuillez indiquer au moins 3 mots-clés.');
         }