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/es/common.json

@@ -1482,6 +1482,9 @@
     "title": "Contactos",
     "search_placeholder": "Buscar contactos...",
     "create_new": "Nuevo contacto",
+    "no_category": "Sin categoría",
+    "category_added": "Contacto añadido a {name}",
+    "category_added_plural": "{count} contactos añadidos a {name}",
     "empty_state": "No hay contactos",
     "empty_state_title": "Sin contactos",
     "empty_state_subtitle": "Crea tu primer contacto o importa desde un archivo vCard",
@@ -1625,7 +1628,8 @@
       "level_low": "Bajo",
       "categories": "Categorías",
       "categories_placeholder": "p. ej., Familia, Amigos, Colegas",
-      "categories_hint": "Separar con comas",
+      "categories_hint": "Escriba para buscar o añadir categorías",
+      "category_add": "Añadir",
       "note": "Notas",
       "note_placeholder": "Agregar una nota...",
       "gender": "Género",