filepond: implement async server-ID upload architecture with nested queue support + PeerTube integration

Replace `storeAsFile:true` with a full async FilePond round-trip pipeline using opaque server-side file IDs.

* Added 4 new PHP endpoints under `/admin/actions/filepond/`:

  * `process.php` — upload/process single file and return opaque `file_id`
  * `revert.php` — delete pending tmp uploads before form submit
  * `load.php` — stream existing files by DB ID for FilePond preload
  * `remove.php` — soft-delete `thesis_files` rows
* `process.php` improvements:

  * accept arbitrary FilePond field names instead of hardcoded `file`
  * support PHP-nested multi-file queue inputs (`queue_file[tfe][]`)
  * explicit unwrapping of nested `$_FILES` structures
  * add `audio/mp3` to audio + `peertube_audio` MIME whitelists
  * immediate upload of `peertube_*` files to PeerTube, returning `peertube:{uuid}` IDs
  * extensive `error_log()` instrumentation for request, CSRF, MIME, upload, and save stages
* `revert.php` now accepts `peertube:` IDs without local cleanup
* `ThesisFileHandler`:

  * add `handleFilePondQueueFiles()` + `handleFilePondSingleFile()`
  * process async uploads from `storage/tmp/filepond/` via opaque `file_id`
  * inline handling of `peertube:{uuid}` IDs with direct `thesis_files` insertion
  * remove obsolete deferred PeerTube queue-processing flow
* `ThesisCreateController` + `ThesisEditController`:

  * gate async path behind `filepond_mode=1`
  * preserve legacy multipart flow as fallback
* `file-upload-filepond.js`:

  * remove `storeAsFile:true`
  * add `buildServerConfig()` for async endpoint wiring
  * fix `syncOrderInput()` to use `serverId`
  * add `onprocessfile` hook
  * add `fileValidateSizeFilterItem` for per-extension size caps
  * preload existing uploads via `data-existing-files` + `server.load`
  * replace static `INPUT_ID_TO_TYPE` map with `data-queue-type`
  * add extensive `console.log()` debugging across upload pipeline stages
* `upload-progress.js`:

  * block form submission while uploads are pending
  * update `collectFileNames()` to read processed FilePond items
* Templates/layout:

  * add `data-queue-type`
  * add `data-existing-files`
  * add global CSRF meta tag outside admin-only context
  * add `filepond_mode` hidden input
  * add CSRF token/meta support for partage pages
  * move website URL field below file upload block
* `.gitignore`: exclude `storage/tmp/` from version control

app/templates/partials/form/fieldset-files.php

@@ -40,7 +40,8 @@ $adminMode = $adminMode ?? false;
             <input type="file" id="tfe-files-input"
                    name="queue_file[tfe][]" multiple
                    accept=".pdf,.jpg,.jpeg,.png,.gif,.webp,.mp4,.webm,.mov,.ogv,.mp3,.ogg,.oga,.wav,.flac,.aac,.m4a,.vtt"
-                   class="tfe-file-picker">
+                   class="tfe-file-picker"
+                   data-queue-type="tfe">
             <small class="admin-file-hint">
                 Types acceptés : PDF · JPG/PNG/GIF/WEBP · MP4/WebM/MOV (vidéo) · MP3/OGG/WAV/FLAC (audio) · ZIP/TAR (archives). Max 500 MB par fichier.
                 Les fichiers <code>.vtt</code> sont des sous-titres et seront associés automatiquement à la vidéo précédente.