feat(custom-fields) : ajoute composable useCustomFieldNameSuggestions

Cache module-level partage entre toutes les instances. Lazy load au
premier appel a load(). invalidate() permet de forcer un refresh apres
creation/modification d'un champ perso.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/app/composables/useCustomFieldNameSuggestions.ts

@@ -0,0 +1,41 @@
+import { ref } from 'vue'
+
+const cache = ref<string[] | null>(null)
+const loading = ref(false)
+
+export function useCustomFieldNameSuggestions() {
+  const api = useApi()
+
+  async function load(force = false): Promise<string[]> {
+    if (cache.value && !force) return cache.value
+    if (loading.value) return cache.value ?? []
+    loading.value = true
+    try {
+      const response = await api.get<string[]>('/api/custom-fields/names')
+      if (response.success && Array.isArray(response.data)) {
+        cache.value = response.data
+      }
+      else {
+        cache.value = cache.value ?? []
+        if (response.error) {
+          console.error('[useCustomFieldNameSuggestions] load failed:', response.error)
+        }
+      }
+      return cache.value
+    }
+    finally {
+      loading.value = false
+    }
+  }
+
+  function invalidate(): void {
+    cache.value = null
+  }
+
+  return {
+    suggestions: cache,
+    loading,
+    load,
+    invalidate,
+  }
+}