chore: gemini api 모델 교체

Author: StoneCAU

src/main/java/shinhan/click/domain/chat/service/ChatService.java

@@ -121,7 +121,7 @@ public SendMessageResponse sendMessage(Long chatId, SendMessageRequest request)
             GenerateContentConfig cfg = GenerateContentConfig.builder()
                     .systemInstruction(Content.fromParts(Part.fromText(buildSystemPrompt(chat))))
                     .build();
-            session = client.chats.create("gemini-2.5-flash", cfg);
+            session = client.chats.create("gemini-1.5-flash", cfg);
             chatSessionRegistry.put(chatId, session);
 
             // 직전 히스토리 시딩 (최적화된 버전)

src/main/java/shinhan/click/domain/futurenote/service/FutureNoteService.java

@@ -214,7 +214,7 @@ private GeneratedFutureNote callGeminiAPI(String prompt) {
                     .build();
 
             // Chat 세션 생성
-            com.google.genai.Chat chat = client.chats.create("gemini-2.5-flash", config);
+            com.google.genai.Chat chat = client.chats.create("gemini-1.5-flash", config);
 
             // 메시지 전송
             GenerateContentResponse response = chat.sendMessage("위의 지시에 따라 JSON 형식으로 완전한 스크립트를 생성해주세요.");

src/main/java/shinhan/click/domain/usernote/service/UserNoteService.java

@@ -271,7 +271,7 @@ private MergeUserNoteResponse performBasicMerge(UserNote firstUserNote, UserNote
 
         try {
             GenerateContentResponse response = client.models.generateContent(
-                    "gemini-2.5-flash",
+                    "gemini-1.5-flash",
                     aiPrompt,
                     null
             );