refactor: session-based incremental TFE upload via HTMX, drop SortableJS

Replace the client-side FileArray + Sortable drag-to-reorder with a
server-side session-based upload flow:

- New endpoints: /partage/upload-tfe-file, /partage/remove-tfe-file
  (and /admin/ variants) — single-file incremental upload via HTMX
  multipart/form-data with progress bar support
- Session storage: uploaded files go to STORAGE_ROOT/uploads/{session_id}/
  with metadata in $_SESSION['tfe_uploads']
- file-upload-queue.js reduced to single-file previews only (couverture,
  note_intention, annexes thumbnails)
- ThesisFileHandler gains handleTfeFilesFromSession + writeTfeFileFromSrc
  + cleanupSessionUploads for final commit from session temp
- Sortable.min.js removed from all script tags; drag handles and ghost
  CSS removed
- No file_orders[]/file_labels[] hidden field injection needed
- Upload queue survives page refresh (server-owned list)

This eliminates the SortableJS dependency entirely while keeping the
same UX: pick files, see them in a queue, remove individual files.

app/src/Controllers/ThesisCreateController.php

@@ -196,7 +196,13 @@ 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);
+
+        // TFE files come from session temp (incremental upload via HTMX)
+        $sessionUploads = $_SESSION['tfe_uploads'] ?? [];
+        $nextNum = $this->handleTfeFilesFromSession($thesisId, $sessionUploads, $folderPath, $filePrefix, 1);
+        // Clear session uploads after successful commit
+        $this->cleanupSessionUploads();
+
         $this->handleAnnexeFiles($thesisId, $files['annexes'] ?? null, $folderPath, $filePrefix, $post);
         // PeerTube file rows don't go on disk, but the uploads themselves are processed separately