feat(S1): iterative conversation for multi-round prompt refinement

- Conversation model: store dialog context (max 10 rounds), JSON messages
- POST /api/prompt/continue: append round, build LLM context from history
- GET/DELETE /api/conversation/🆔 retrieve or clear conversation
- Vue: refine input card below result, round counter, reset button
- Vue: continuePrompt API with conversation_id tracking

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

vue-app/src/api/modules/prompt.ts

@@ -17,3 +17,21 @@ export function fetchTemplatesByCategory(category: string) {
 export function generatePrompt(body: { input_text: string; template_id: number | null; max_tokens?: number }) {
   return client.post<GeneratePromptResponse>('/api/prompt/generate', body).then((r) => r.data)
 }
+
+export interface ContinuePromptResponse {
+  success: boolean
+  message?: string
+  conversation_id: number
+  generated_text: string
+  rounds: number
+  prompt?: { id: number; input_text: string; generated_text: string }
+}
+
+export function continuePrompt(body: {
+  conversation_id?: number | null
+  previous_result: string
+  refine_instruction: string
+  template_id?: number | null
+}) {
+  return client.post<ContinuePromptResponse>('/api/prompt/continue', body).then((r) => r.data)
+}