Contenus: add Mots-clés fieldset mirroring Langues, keep dedicated page button as backup, add Annuler cancel button to both bulk action bars, limit both table wraps to max-height:50vh with overflow scroll

TODO.md

@@ -1,5 +1,13 @@
 # Current tasks
 
+## Mots-clés fieldset in contenus
+- [x] Create contenus-motscles-fragment.php (tags fragment mirroring langues)
+- [x] Add Mots-clés fieldset to contenus template (search + table + bulk actions)
+- [x] Keep button linking to dedicated tags.php page as backup
+- [x] Add "Annuler" cancel button to both langues and mots-clés bulk action bars
+- [x] Add max-height:50vh + overflow-y:auto to both table wraps
+- [ ] Deploy: just deploy
+
 ## Tmp file cleanup (stale filepond + _trash)
 - [x] Session-based detection: check manifest session_id against PHP session files
 - [x] DB-based detection for _trash: check thesis_files row still exists
@@ -10,6 +18,15 @@
 - [x] .gitignore: exclude tmp/filepond/* and tmp/_trash/*
 - [ ] Deploy: just deploy
 
+## Index page improvements
+- [x] Remove 'Mots-clés' button from toolbar
+- [x] Move export to bulk selection bar (Exporter CSV + Exporter fichiers buttons)
+- [x] Export dispatcher accepts ?ids= for per-selection filtering
+- [x] All ExportController/Database export methods accept optional thesisIds
+- [x] Graceful error when ZipArchive extension missing (php8.4-zip not installed)
+- [x] Move DB export (SQLite download) to paramètres → Maintenance section
+- [x] Sticky thead on index table (position: sticky, top: 0, z-index: 5)
+
 ## Dialog & trash page margins
 - [x] Add admin-dialog__body CSS rule with padding + margin resets
 - [x] Add admin-dialog__stats + admin-dialog__hint classes