Refactor: Eliminate code duplication for currency conversion and item pricing

- Add static calculateItemValueSC() and getItemValueSC() helpers to MournbladeCYD2Utility
  to centralize currency conversion logic (1 PO = 100 SC, 1 PA = 10 SC)
- Refactor computeRichesse() and computeValeurEquipement() in Actor to use shared helpers
- Add localizeAllegiance Handlebars helper to display allegiance values localized
  (tous->Tous, chaos->Chaos, loi->Loi, betes->Bêtes, elementaires->Élémentaires)
- Add joinPredilections helper to fix comma display after single Predilection
- Create BaseItemWithPriceDataModel base class for items with pricing fields
  (prixpo, prixca, prixsc, rarete, quantite, equipped)
- Update arme, equipement, protection, monnaie models to extend base class
- Update actor-sheet and creature-sheet templates to use new helpers
- Update partial-item-prix.hbs to display total item value in SC
- Add item-base-sheet.hbs template for future item sheet inheritance

Fixes:
- Allegiance values now display properly localized in Dons & Pactes tabs
- Predilections no longer show trailing comma with single entry
- Equipment value totals now update correctly when items are added/modified
- Currency conversion logic centralized and consistent across the system

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

modules/mournblade-cyd2-utility.js

@@ -54,13 +54,49 @@ export class MournbladeCYD2Utility {
     // Conversion selon le lore Mournblade :
     // 1 SA (Sou d'Argent / Pièce d'Argent) = 10 PB (Pièces de Bronze / Sous de Cuivre)
     // 1 PO (Pièce d'Or) = 10 SA = 100 PB
-    // Donc : 1 CA = 10 SC, 1 PO = 100 SC
-    Handlebars.registerHelper('calculateItemValueSC', function (prixpo, prixca, prixsc) {
+    // Donc : 1 PA (Pièce d'Argent) = 10 SC, 1 PO (Pièce d'Or) = 100 SC
+    static calculateItemValueSC(prixpo, prixca, prixsc) {
       const po = parseInt(prixpo) || 0;
       const ca = parseInt(prixca) || 0;
       const sc = parseInt(prixsc) || 0;
       return po * 100 + ca * 10 + sc;
+    }
+
+    // Helper Handlebars pour les templates
+    Handlebars.registerHelper('calculateItemValueSC', function (prixpo, prixca, prixsc) {
+      return MournbladeCYD2Utility.calculateItemValueSC(prixpo, prixca, prixsc);
     });
+
+    // Helper pour localiser les valeurs d'allégeance
+    Handlebars.registerHelper('localizeAllegiance', function (value) {
+      if (!value) return value;
+      const allegianceMap = {
+        'tous': 'MNBL.all',
+        'chaos': 'MNBL.chaos',
+        'loi': 'MNBL.law',
+        'betes': 'MNBL.betes',
+        'elementaires': 'MNBL.elementaires',
+        'balance': 'MNBL.balance'
+      };
+      const key = allegianceMap[value?.toLowerCase?.()] || value;
+      return game.i18n?.localize?.(key) ?? value;
+    });
+
+    // Helper pour joindre les prédilections sans virgule superflue
+    Handlebars.registerHelper('joinPredilections', function (predilections) {
+      if (!predilections || !Array.isArray(predilections)) return '';
+      return predilections
+        .filter(pred => pred && pred.acquise && !pred.used)
+        .map(pred => pred.name)
+        .join(', ');
+    });
+
+    // Helper pour calculer la valeur SC d'un item avec quantité
+    static getItemValueSC(item) {
+      const value = this.calculateItemValueSC(item.system?.prixpo, item.system?.prixca, item.system?.prixsc);
+      const quantity = item.system?.quantite || 1;
+      return value * quantity;
+    }
     
     Handlebars.registerHelper('select', function(value, options) {
       const html = options.fn(this);