feat: calculs tableaux Structured Views + Link Preview + fixes

- Calculs en pied de tableau : Somme/Moyenne/Min/Max/Compte, cliquable pour changer
- Link Preview : métadonnées persistées + texte indexable pour recherche/embeddings
- Fix: bg-memento-paper → bg-card (dark mode) sur dialogs Structured Views
- Fix: bouton Ajouter un champ → brand-accent au lieu de primary
- Calendar view retiré du sélecteur (non pertinent)

memento-note/locales/en.json

@@ -2647,6 +2647,8 @@
     "deleteProperty": "Delete field",
     "deletePropertyTitle": "Delete this field?",
     "deletePropertyConfirm": "The field \"{name}\" and all its values on notes in this notebook will be removed. This cannot be undone.",
+    "calculations": "Calculations",
+    "calcClickToChange": "Click to change calculation type (Sum, Average, Min, Max, Count, None)",
     "deletePropertySuccess": "Field deleted",
     "cellEmpty": "—",
     "multiselectPick": "Choose…",