Implémentation complète du multilingue FR/EN

- Installation vue-i18n v11 et création des fichiers de traduction (fr.json, en.json)
- Création store locale avec détection hiérarchique (URL > localStorage > navigator)
- Modification des routes avec préfixe /:locale? optionnel
- Toggle FR/EN dans Menu.vue avec synchronisation immédiate
- Traduction de ~200 textes dans 27 composants Vue
- Suppression des labels hardcodés en français côté backend
- Ajout route Kirby catch-all en/(:all?) pour /en/ URLs
- Helper addLocalePrefix() pour préserver locale dans liens dialogs
- Traduction pseudo-élément CSS via data attribute

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

package-lock.json

@@ -19,6 +19,7 @@
         "three": "^0.168.0",
         "uniqid": "^5.4.0",
         "vue": "^3.5.6",
+        "vue-i18n": "^11.2.8",
         "vue-router": "^4.4.5"
       },
       "devDependencies": {
@@ -542,6 +543,50 @@
         "@swc/helpers": "^0.5.0"
       }
     },
+    "node_modules/@intlify/core-base": {
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+      "resolved": "https://registry.npmjs.org/@intlify/core-base/-/core-base-11.2.8.tgz",
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+      "license": "MIT",
+      "dependencies": {
+        "@intlify/message-compiler": "11.2.8",
+        "@intlify/shared": "11.2.8"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      }
+    },
+    "node_modules/@intlify/message-compiler": {
+      "version": "11.2.8",
+      "resolved": "https://registry.npmjs.org/@intlify/message-compiler/-/message-compiler-11.2.8.tgz",
+      "integrity": "sha512-A5n33doOjmHsBtCN421386cG1tWp5rpOjOYPNsnpjIJbQ4POF0QY2ezhZR9kr0boKwaHjbOifvyQvHj2UTrDFQ==",
+      "license": "MIT",
+      "dependencies": {
+        "@intlify/shared": "11.2.8",
+        "source-map-js": "^1.0.2"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      }
+    },
+    "node_modules/@intlify/shared": {
+      "version": "11.2.8",
+      "resolved": "https://registry.npmjs.org/@intlify/shared/-/shared-11.2.8.tgz",
+      "integrity": "sha512-l6e4NZyUgv8VyXXH4DbuucFOBmxLF56C/mqh2tvApbzl2Hrhi1aTDcuv5TKdxzfHYmpO3UB0Cz04fgDT9vszfw==",
+      "license": "MIT",
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      }
+    },
     "node_modules/@jridgewell/sourcemap-codec": {
       "version": "1.5.5",
       "resolved": "https://registry.npmjs.org/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.5.5.tgz",
@@ -1857,6 +1902,26 @@
         }
       }
     },
+    "node_modules/vue-i18n": {
+      "version": "11.2.8",
+      "resolved": "https://registry.npmjs.org/vue-i18n/-/vue-i18n-11.2.8.tgz",
+      "integrity": "sha512-vJ123v/PXCZntd6Qj5Jumy7UBmIuE92VrtdX+AXr+1WzdBHojiBxnAxdfctUFL+/JIN+VQH4BhsfTtiGsvVObg==",
+      "license": "MIT",
+      "dependencies": {
+        "@intlify/core-base": "11.2.8",
+        "@intlify/shared": "11.2.8",
+        "@vue/devtools-api": "^6.5.0"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      },
+      "peerDependencies": {
+        "vue": "^3.0.0"
+      }
+    },
     "node_modules/vue-router": {
       "version": "4.5.1",
       "resolved": "https://registry.npmjs.org/vue-router/-/vue-router-4.5.1.tgz",