feat: fix file deletion on save + trash policy + documents/ prefix + relink browser

1. note_intention: Delete old file only when a genuinely new upload arrives
   (32-char hex file_id), not when the FilePond pool preserves an existing
   file by sending its DB integer ID.  Previously the DB integer ID
   triggered $hasNewNote=true, which deleted the existing note_intention
   from disk+DB, then handleFilePondSingleFile couldn't re-process it
   because the regex requires a hex pattern.  Same fix applied to cover.

2. All file deletions now use deleteThesisFileToTrash() which renames
   files to tmp/_trash/ instead of unlinking.  The trash preserves
   original filenames prefixed with DB id for traceability.  Skips
   website URLs and PeerTube refs (no disk file).

3. Storage prefix changed from theses/ to documents/ to reflect that
   the folder holds all document types (determined by file_type in DB).
   MediaController visibility gate supports both prefixes for backward
   compat with existing files.

4. File browser + relink feature for orphaned files:
   - /admin/fragments/file-browser.php — HTMX tree browser for
     storage/documents/ and storage/theses/
   - /admin/actions/filepond/relink.php — POST endpoint that inserts
     a thesis_files row pointing to existing on-disk file
   - Per-pool "📂 Relier" buttons (edit mode only)
   - JS: XamxamOpenFileBrowser / XamxamRelinkFile with FilePond integration
   - CSS: .relink-modal dialog + .file-browser tree styles

app/public/assets/css/form.css

@@ -1023,6 +1023,19 @@
   pointer-events: none;
 }
 
+/* ── Jury autocomplete dropdown (positioned within .admin-jury-lecteurs) ──── */
+.admin-jury-lecteurs[data-jury-autocomplete] {
+  position: relative;
+}
+
+.admin-jury-lecteurs .jury-suggestions {
+  position: absolute;
+  top: auto;
+  left: 0;
+  right: 0;
+  margin-top: 2px;
+}
+
 /* Individual suggestion item */
 .tag-search-item {
   display: flex;
@@ -1340,3 +1353,134 @@ legend {
   color: var(--text-secondary);
   font-style: italic;
 }
+
+/* ── File browser (relink) ──────────────────────────────────────── */
+
+.file-browser-trigger {
+  margin-top: var(--space-2xs);
+  font-size: var(--step--2);
+}
+
+.relink-modal {
+  width: min(90vw, 700px);
+  max-height: 80vh;
+  border: 1px solid var(--border);
+  border-radius: var(--radius);
+  background: var(--bg-primary);
+  padding: 0;
+  overflow: hidden;
+  color: var(--text-primary);
+}
+.relink-modal::backdrop {
+  background: rgba(0,0,0,0.5);
+}
+.relink-modal-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: var(--space-s) var(--space-m);
+  border-bottom: 1px solid var(--border);
+  background: var(--bg-secondary);
+}
+.relink-modal-header h3 {
+  margin: 0;
+  font-size: var(--step-0);
+}
+.relink-modal-footer {
+  padding: var(--space-xs) var(--space-m);
+  border-top: 1px solid var(--border);
+  background: var(--bg-secondary);
+}
+#relink-modal-body {
+  padding: var(--space-s) var(--space-m);
+  overflow-y: auto;
+  max-height: 60vh;
+}
+
+/* ── File browser tree ─────────────────────────────────────────── */
+
+.file-browser {
+  font-size: var(--step--1);
+}
+.file-browser-hint,
+.file-browser-empty,
+.file-browser-loading,
+.file-browser-error {
+  color: var(--text-secondary);
+  text-align: center;
+  padding: var(--space-m);
+}
+.file-browser-error {
+  color: var(--error);
+}
+.file-browser-breadcrumb {
+  display: flex;
+  align-items: center;
+  gap: var(--space-2xs);
+  flex-wrap: wrap;
+  padding-bottom: var(--space-s);
+  margin-bottom: var(--space-s);
+  border-bottom: 1px solid var(--border);
+  font-size: var(--step--2);
+}
+.file-browser-breadcrumb a {
+  color: var(--accent-blue, var(--link));
+  text-decoration: none;
+}
+.file-browser-breadcrumb a:hover {
+  text-decoration: underline;
+}
+.file-browser-sep {
+  color: var(--text-tertiary);
+}
+
+.file-browser-list {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+}
+.file-browser-entry {
+  border-bottom: 1px solid var(--border-subtle);
+}
+.file-browser-entry a,
+.file-browser-select-btn {
+  display: flex;
+  align-items: center;
+  gap: var(--space-xs);
+  width: 100%;
+  padding: var(--space-xs) var(--space-2xs);
+  text-decoration: none;
+  color: var(--text-primary);
+  background: none;
+  border: none;
+  cursor: pointer;
+  font-size: var(--step--1);
+  text-align: left;
+  transition: background 0.15s;
+}
+.file-browser-entry a:hover,
+.file-browser-select-btn:hover {
+  background: var(--bg-secondary);
+}
+.file-browser-icon {
+  flex-shrink: 0;
+  font-size: var(--step-0);
+}
+.file-browser-name {
+  flex: 1;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.file-browser-size {
+  flex-shrink: 0;
+  color: var(--text-tertiary);
+  font-size: var(--step--2);
+  font-variant-numeric: tabular-nums;
+}
+.file-browser-file .file-browser-select-btn {
+  color: var(--accent-green, var(--success));
+}
+.file-browser-file .file-browser-select-btn:hover {
+  background: var(--bg-secondary);
+}