feat(be): AI 챗 컨트롤러 및 REST API 엔드포인트 구현

- AiChatController 6개 엔드포인트 완성
  * GET /sessions (세션 목록)
  * POST /sessions (세션 생성)
  * DELETE /sessions/{id} (세션 삭제)
  * GET /sessions/{id}/messages (메시지 조회)
  * POST /sessions/{id}/messages (메시지 전송)
  * PATCH /sessions/{id}/title (제목 수정)

- Service Layer Entity 반환으로 리팩토링
- Controller Layer DTO 변환 책임 분리
- getSessionWithOwnershipCheck 헬퍼 메서드 적용
- ChatController → AiChatController 리네임
- DTO 구조 정리 및 신규 DTO 추가

Author: Mrbaeksang

docs/api-specification.yaml

@@ -521,6 +521,50 @@ paths:
                           aiMessage:
                             $ref: '#/components/schemas/AiChatMessage'
 
+  /api/aichat/sessions/{sessionId}/title:
+    patch:
+      tags:
+        - aichat
+      summary: AI 채팅 세션 제목 수정
+      description: AI 채팅 세션의 제목을 사용자가 직접 수정합니다
+      parameters:
+        - name: sessionId
+          in: path
+          required: true
+          schema:
+            type: integer
+            format: int64
+          description: AI 채팅 세션 ID
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              required:
+                - title
+              properties:
+                title:
+                  type: string
+                  maxLength: 100
+                  description: 새로운 세션 제목
+      responses:
+        '200':
+          description: 제목 수정 성공
+          content:
+            application/json:
+              schema:
+                allOf:
+                  - $ref: '#/components/schemas/ApiResponse'
+                  - type: object
+                    properties:
+                      data:
+                        $ref: '#/components/schemas/AiChatSession'
+        '404':
+          description: 세션을 찾을 수 없음
+        '403':
+          description: 권한 없음
+
   # ===================
   # User Chat Domain APIs
   # ===================

src/main/kotlin/com/back/koreaTravelGuide/domain/ai/aiChat/controller/AiChatController.kt

@@ -0,0 +1,85 @@
+package com.back.koreaTravelGuide.domain.ai.aiChat.controller
+
+import com.back.koreaTravelGuide.domain.ai.aiChat.dto.AiChatRequest
+import com.back.koreaTravelGuide.domain.ai.aiChat.dto.AiChatResponse
+import com.back.koreaTravelGuide.domain.ai.aiChat.dto.SessionMessagesResponse
+import com.back.koreaTravelGuide.domain.ai.aiChat.dto.SessionsResponse
+import com.back.koreaTravelGuide.domain.ai.aiChat.dto.UpdateSessionTitleRequest
+import com.back.koreaTravelGuide.domain.ai.aiChat.dto.UpdateSessionTitleResponse
+import com.back.koreaTravelGuide.domain.ai.aiChat.service.AiChatService
+import org.springframework.web.bind.annotation.DeleteMapping
+import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.PatchMapping
+import org.springframework.web.bind.annotation.PathVariable
+import org.springframework.web.bind.annotation.PostMapping
+import org.springframework.web.bind.annotation.RequestBody
+import org.springframework.web.bind.annotation.RequestMapping
+import org.springframework.web.bind.annotation.RequestParam
+import org.springframework.web.bind.annotation.RestController
+
+@RestController
+@RequestMapping("/api/aichat")
+class AiChatController(
+    private val aiChatService: AiChatService,
+) {
+    @GetMapping("/sessions")
+    fun getSessions(
+        @RequestParam userId: Long,
+    ): List<SessionsResponse> {
+        return aiChatService.getSessions(userId).map {
+            SessionsResponse(it.id!!, it.sessionTitle)
+        }
+    }
+
+    @PostMapping("/sessions")
+    fun createSession(
+        @RequestParam userId: Long,
+    ): SessionsResponse {
+        val session = aiChatService.createSession(userId)
+        return SessionsResponse(session.id!!, session.sessionTitle)
+    }
+
+    @DeleteMapping("/sessions/{sessionId}")
+    fun deleteSession(
+        @PathVariable sessionId: Long,
+        @RequestParam userId: Long,
+    ) {
+        aiChatService.deleteSession(sessionId, userId)
+    }
+
+    @GetMapping("/sessions/{sessionId}/messages")
+    fun getSessionMessages(
+        @PathVariable sessionId: Long,
+        @RequestParam userId: Long,
+    ): List<SessionMessagesResponse> {
+        val messages = aiChatService.getSessionMessages(sessionId, userId)
+        return messages.map {
+            SessionMessagesResponse(it.content, it.senderType)
+        }
+    }
+
+    @PostMapping("/sessions/{sessionId}/messages")
+    fun sendMessage(
+        @PathVariable sessionId: Long,
+        @RequestParam userId: Long,
+        @RequestBody request: AiChatRequest,
+    ): AiChatResponse {
+        val (userMessage, aiMessage) = aiChatService.sendMessage(sessionId, userId, request.message)
+        return AiChatResponse(
+            userMessage = userMessage.content,
+            aiMessage = aiMessage.content,
+        )
+    }
+
+    @PatchMapping("/sessions/{sessionId}/title")
+    fun updateSessionTitle(
+        @PathVariable sessionId: Long,
+        @RequestParam userId: Long,
+        @RequestBody request: UpdateSessionTitleRequest,
+    ): UpdateSessionTitleResponse {
+        val updatedSession = aiChatService.updateSessionTitle(sessionId, userId, request.newTitle)
+        return UpdateSessionTitleResponse(
+            newTitle = updatedSession.sessionTitle,
+        )
+    }
+}

src/main/kotlin/com/back/koreaTravelGuide/domain/ai/aiChat/controller/ChatController.kt

@@ -0,0 +1,5 @@
+package com.back.koreaTravelGuide.domain.ai.aiChat.dto
+
+data class AiChatRequest(
+    val message: String,
+)

src/main/kotlin/com/back/koreaTravelGuide/domain/ai/aiChat/dto/AiChatRequest.kt

@@ -0,0 +1,6 @@
+package com.back.koreaTravelGuide.domain.ai.aiChat.dto
+
+data class AiChatResponse(
+    val userMessage: String,
+    val aiMessage: String,
+)

src/main/kotlin/com/back/koreaTravelGuide/domain/ai/aiChat/dto/AiChatResponse.kt

@@ -0,0 +1,5 @@
+package com.back.koreaTravelGuide.domain.ai.aiChat.dto
+
+data class DeleteAiChatRequest(
+    val sessionId: Long,
+)

src/main/kotlin/com/back/koreaTravelGuide/domain/ai/aiChat/dto/ChatRequest.kt

@@ -0,0 +1,8 @@
+package com.back.koreaTravelGuide.domain.ai.aiChat.dto
+
+import com.back.koreaTravelGuide.domain.ai.aiChat.entity.SenderType
+
+data class SessionMessagesResponse(
+    val content: String,
+    val senderType: SenderType,
+)

src/main/kotlin/com/back/koreaTravelGuide/domain/ai/aiChat/dto/ChatResponse.kt

@@ -0,0 +1,6 @@
+package com.back.koreaTravelGuide.domain.ai.aiChat.dto
+
+data class SessionsResponse(
+    val sessionId: Long,
+    val sessionTitle: String,
+)