feat: AI(Gemini) 스팟 궁합 메이트 추천

체크인한 스팟의 활성 강아지(Redis 24h) 중 내 강아지와 사이좋게 지낼 만한
강아지만 Gemini 로 골라 궁합점수·이유와 함께 반환.
GET /api/spots/{id}/ai-mates?dogId=...

- GeminiClient: responseSchema 로 구조화 JSON 강제(gemini-flash-latest)
- MateAiService: 후보 성향/크기로 프롬프트 구성, 후보 밖 dogId(환각) 필터, 점수 내림차순
- application.yml: app.ai.gemini (env GEMINI_API_KEY, 미설정 시 503)
- 키 없이도 컨텍스트/테스트 통과 → CI 안전

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/main/java/com/dog/dognation/api/SpotController.java

@@ -1,11 +1,13 @@
 package com.dog.dognation.api;
 
+import com.dog.dognation.api.dto.SpotDtos.AiMateResponse;
 import com.dog.dognation.api.dto.SpotDtos.CheckInRequest;
 import com.dog.dognation.api.dto.SpotDtos.CheckInResponse;
 import com.dog.dognation.api.dto.SpotDtos.MateResponse;
 import com.dog.dognation.api.dto.SpotDtos.ReviewCreateRequest;
 import com.dog.dognation.api.dto.SpotDtos.ReviewResponse;
 import com.dog.dognation.api.dto.SpotDtos.SpotResponse;
+import com.dog.dognation.domain.spot.MateAiService;
 import com.dog.dognation.domain.spot.SpotService;
 import jakarta.validation.Valid;
 import org.springframework.http.HttpStatus;
@@ -15,6 +17,7 @@ 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;
 
 import java.util.List;
@@ -24,9 +27,11 @@ import java.util.List;
 public class SpotController {
 
     private final SpotService spotService;
+    private final MateAiService mateAiService;
 
-    public SpotController(SpotService spotService) {
+    public SpotController(SpotService spotService, MateAiService mateAiService) {
         this.spotService = spotService;
+        this.mateAiService = mateAiService;
     }
 
     /** 스팟 목록 */
@@ -50,6 +55,12 @@ public class SpotController {
         return spotService.activeMates(id).stream().map(MateResponse::from).toList();
     }
 
+    /** AI 궁합 메이트 추천 — 내 강아지(dogId)와 사이좋게 지낼 만한 스팟 내 강아지 목록 */
+    @GetMapping("/{id}/ai-mates")
+    public List<AiMateResponse> aiMates(@PathVariable Long id, @RequestParam Long dogId) {
+        return mateAiService.compatibleMates(id, dogId);
+    }
+
     /** 스팟 한줄평 목록 */
     @GetMapping("/{id}/reviews")
     public List<ReviewResponse> reviews(@PathVariable Long id) {