feat: implémentation complète du système Célestopol 1922 pour FoundryVTT v13

- DataModels (character, npc, anomaly, aspect, attribute, equipment)
- ApplicationV2 sheets (character 5 tabs, npc 3 tabs, 4 item sheets)
- DialogV2 pour les jets de dés avec phase de lune
- Templates Handlebars complets (fiches PJ/PNJ, items, jet, chat)
- Styles LESS → CSS compilé (thème vert foncé / orange CopaseticNF)
- i18n fr.json complet (clés CELESTOPOL.*)
- Point d'entrée fvtt-celestopol.mjs avec hooks init/ready
- Assets : polices CopaseticNF, images UI, icônes items
- Mise à jour copilot-instructions.md avec l'architecture réelle

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

module/applications/sheets/base-item-sheet.mjs

@@ -0,0 +1,39 @@
+const { HandlebarsApplicationMixin } = foundry.applications.api
+
+export default class CelestopolItemSheet extends HandlebarsApplicationMixin(foundry.applications.sheets.ItemSheetV2) {
+  /** @override */
+  static DEFAULT_OPTIONS = {
+    classes: ["fvtt-celestopol", "item"],
+    position: { width: 580, height: "auto" },
+    form: { submitOnChange: true },
+    window: { resizable: true },
+    actions: {
+      editImage: CelestopolItemSheet.#onEditImage,
+    },
+  }
+
+  /** @override */
+  async _prepareContext() {
+    return {
+      fields:       this.document.schema.fields,
+      systemFields: this.document.system.schema.fields,
+      item:         this.document,
+      system:       this.document.system,
+      source:       this.document.toObject(),
+      isEditable:   this.isEditable,
+    }
+  }
+
+  static async #onEditImage(event, target) {
+    const attr    = target.dataset.edit
+    const current = foundry.utils.getProperty(this.document, attr)
+    const fp = new FilePicker({
+      current,
+      type: "image",
+      callback: (path) => this.document.update({ [attr]: path }),
+      top:  this.position.top + 40,
+      left: this.position.left + 10,
+    })
+    return fp.browse()
+  }
+}