Guard no-JS file uploads: disabled filepond_mode by default, server-side fallback

The partage/admin form had a hardcoded filepond_mode=1 hidden input,
so without JavaScript the server always entered the FilePond async
path — which found no hex IDs and silently dropped all files.

Three-layer fix:
1. HTML: filepond_mode input starts disabled with value=0; JS enables
   it and sets value=1 on DOMContentLoaded (and after HTMX swaps).
   Disabled inputs aren't submitted → server gets no filepond_mode
   → naturally falls to legacy  path.
2. JS: enableFilepondMode() called on page load and hx:afterSwap so
   FilePond-enhanced forms always send filepond_mode=1.
3. Server (defense-in-depth): ThesisFileHandler::hasFilePondQueueData()
   scans POST['queue_file'] for 32-char hex IDs; ThesisCreateController
   and ThesisEditController use it alongside filepond_mode, so even if
   the flag somehow arrives without async upload IDs, the  path
   takes over.

app/src/Controllers/ThesisEditController.php

@@ -359,8 +359,12 @@ class ThesisEditController
             mkdir($dirAbs, 0755, true);
         }
 
+        // Determine upload path: FilePond async (JS enabled, hex IDs present)
+        // vs. legacy multipart. Defense-in-depth fallback for no-JS scenarios.
+        $useFilePond = !empty($post['filepond_mode']) && $this->hasFilePondQueueData($post);
+
         // ── Cover image (outside transaction — filesystem op) ─────────────────
-        if (!empty($post['filepond_mode'])) {
+        if ($useFilePond) {
             // Delete old cover only if a genuinely new cover was uploaded (hex file_id).
             // Existing cover preserved in FilePond sends its DB integer ID — skip.
             $coverIdRaw = ($post['queue_file']['cover'] ?? null);
@@ -387,7 +391,7 @@ class ThesisEditController
         }
 
         // ── Note d'intention (replace if uploaded) ────────────────────────────
-        if (!empty($post['filepond_mode'])) {
+        if ($useFilePond) {
             // Only delete + replace if a genuinely new file was uploaded (hex file_id).
             // Existing files preserved in the FilePond pool send their DB integer ID;
             // we must NOT delete them — they're already stored.
@@ -454,7 +458,7 @@ class ThesisEditController
             }
         }
 
-        if (!empty($post['filepond_mode'])) {
+        if ($useFilePond) {
             // New path: files already on server via async FilePond uploads
             $nextNum = $tfeCount + 1;
             $nextNum = $this->handleFilePondQueueFiles($thesisId, $post, 'tfe', $folderPath, $filePrefix, $nextNum);