feat(contacts): add no-category filter, drag-drop to category, and category combo box

- Add 'No Category' sidebar item to filter uncategorized contacts
- Categories section now always visible (not just when keywords exist)
- Add drag-and-drop support on category items in sidebar to assign keywords
- Fix effectAllowed mismatch (move -> copyMove) for category drop targets
- Replace plain text categories input with combo box in contact edit form
  - Shows existing categories as clickable suggestions
  - Displays assigned categories as removable badges
  - Supports adding new categories inline
- Add translations for all 8 locales

locales/fr/common.json

@@ -1482,6 +1482,9 @@
     "title": "Contacts",
     "search_placeholder": "Rechercher des contacts...",
     "create_new": "Nouveau contact",
+    "no_category": "Sans catégorie",
+    "category_added": "Contact ajouté à {name}",
+    "category_added_plural": "{count} contacts ajoutés à {name}",
     "empty_state": "Aucun contact",
     "empty_state_title": "Aucun contact",
     "empty_state_subtitle": "Créez votre premier contact ou importez depuis un fichier vCard",
@@ -1625,7 +1628,8 @@
       "level_low": "Faible",
       "categories": "Catégories",
       "categories_placeholder": "p. ex., Famille, Amis, Collègues",
-      "categories_hint": "Séparer par des virgules",
+      "categories_hint": "Tapez pour rechercher ou ajouter",
+      "category_add": "Ajouter",
       "note": "Notes",
       "note_placeholder": "Ajouter une note...",
       "gender": "Genre",