Two critical fixes:
1. Relink flow no longer destroys/recreates FilePond instances:
The relink (XamxamRelinkFile) and PeerTube relink (XamxamRelinkPeerTube)
previously refreshed the entire fichiers fragment via HTMX after
pond.addFile(). This triggered destroyFilePondsIn on ALL pools, which
could fire server.remove callbacks and move existing files to corbeille.
Now just closes the modal — the file is already added to the pool in-place,
and syncOrderInput creates the hidden form input.
2. Cleanup page « Corbeille (restaurable) » now actually shows files:
_cleanup-stats-data.php previously classified trash files by checking if
the thesis_files DB row still existed. But both deleteThesisFileToTrash
and FilepondHandler::handleRemove DELETE the DB row. So ALL trash files
appeared as `stale` (not restorable). Now uses the JSON sidecar file
presence as the classification criterion — if the sidecar exists and is
recent, the file is restorable regardless of DB row state.
Also removed unused DB query from _cleanup-stats-data.php.
