Phase 25: RAG sources in collapsible box + Korean thinking enforcement

- agent_service: yield {"__sources": [...]} token instead of __meta for sources
- agent_service: inject Korean-only rule at top of system message before date
- config.py: strengthen Korean thinking instruction in system prompt
- ROADMAP: add Phase 25 entry

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

services/agent/agent_service.py

@@ -79,7 +79,12 @@ class AgentService:
 
         async def call_model(state: MessagesState, config: RunnableConfig) -> dict:
             from datetime import date
-            system_content = f"오늘 날짜: {date.today().isoformat()}\n\n" + self._system_prompt
+            system_content = (
+                "【언어 규칙】모든 사고 과정(thinking)과 답변을 반드시 한국어로 작성하세요. "
+                "영어 사용 금지. Think in Korean only.\n\n"
+                f"오늘 날짜: {date.today().isoformat()}\n\n"
+                + self._system_prompt
+            )
             if self._profile_repo:
                 profile = self._profile_repo.get_all(self._user_id)
                 if profile:
@@ -367,11 +372,13 @@ class AgentService:
                 print(f"[Agent] 대화 저장 실패: {e}")
 
         if self._rag_show_sources and self._source_buffer:
-            yield {"__meta": "\n\n[참고 문서]\n"}
+            sources = []
             for src in self._source_buffer:
-                filename = os.path.basename(src["source"])
-                page = f" {src['page']}페이지" if "page" in src else ""
-                yield {"__meta": f"- {filename}{page}\n"}
+                entry = {"filename": os.path.basename(src["source"])}
+                if "page" in src:
+                    entry["page"] = src["page"]
+                sources.append(entry)
+            yield {"__sources": sources}
 
     def reset(self) -> None:
         """새 thread_id로 대화 히스토리를 초기화한다."""