feat(02-01): prompt editor UI with types, hooks, page, route, sidebar

- Add PromptInfo, PromptListResponse, PromptDetail types
- Add usePromptList, usePrompt, useSavePrompt, useResetPrompt hooks
- Create PromptEditor page with two-column layout, live variables
- Add /prompt-editor route in App.tsx
- Add Prompt Editor nav item with Pencil icon in Sidebar
- TypeScript compiles without errors

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/api/hooks.ts

@@ -19,6 +19,8 @@ import type {
   GenerateResponse,
   JobStatus,
   PostResult,
+  PromptDetail,
+  PromptListResponse,
   Settings,
   SettingsStatus,
 } from '../types'
@@ -184,3 +186,51 @@ export function useDownloadEditedCsv() {
     },
   })
 }
+
+// ---------------------------------------------------------------------------
+// Prompt Editor
+// ---------------------------------------------------------------------------
+
+/** Lista tutti i prompt disponibili con flag modificato/default. */
+export function usePromptList() {
+  return useQuery<PromptListResponse>({
+    queryKey: ['prompts'],
+    queryFn: () => apiGet<PromptListResponse>('/prompts'),
+    staleTime: 30_000,
+  })
+}
+
+/** Carica contenuto + variabili di un singolo prompt. */
+export function usePrompt(name: string | null) {
+  return useQuery<PromptDetail>({
+    queryKey: ['prompts', name],
+    queryFn: () => apiGet<PromptDetail>(`/prompts/${name}`),
+    enabled: !!name,
+    staleTime: 0, // Sempre fresco dopo edit
+  })
+}
+
+/** Salva il contenuto modificato di un prompt. */
+export function useSavePrompt() {
+  const queryClient = useQueryClient()
+  return useMutation<PromptDetail, Error, { name: string; content: string }>({
+    mutationFn: ({ name, content }) =>
+      apiPut<PromptDetail>(`/prompts/${name}`, { content }),
+    onSuccess: (data) => {
+      queryClient.invalidateQueries({ queryKey: ['prompts'] })
+      queryClient.setQueryData(['prompts', data.name], data)
+    },
+  })
+}
+
+/** Reset un prompt al default originale. */
+export function useResetPrompt() {
+  const queryClient = useQueryClient()
+  return useMutation<PromptDetail, Error, string>({
+    mutationFn: (name) => apiPost<PromptDetail>(`/prompts/${name}/reset`),
+    onSuccess: (data) => {
+      queryClient.invalidateQueries({ queryKey: ['prompts'] })
+      queryClient.setQueryData(['prompts', data.name], data)
+    },
+  })
+}