feat: 게시글 인라인 이미지 서버 업로드(DB 저장) — base64 대체

- board_image 테이블 + BoardImageController/Service/Mapper
  · POST /api/board/images(로그인) → {url:/api/images/{id}}
  · GET  /api/images/{id}(공개, img src 로 로드) — 1년 캐시
- 본문엔 짧은 URL 만 들어가 글이 비대해지지 않음

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/java/com/sb/web/board/controller/BoardImageController.java

@@ -0,0 +1,57 @@
+package com.sb.web.board.controller;
+
+import com.sb.web.auth.dto.SessionUser;
+import com.sb.web.auth.web.AuthInterceptor;
+import com.sb.web.board.domain.BoardImage;
+import com.sb.web.board.service.BoardImageService;
+import com.sb.web.common.exception.ApiException;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.CacheControl;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+import org.springframework.web.multipart.MultipartFile;
+
+import java.io.IOException;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * 게시글 인라인 이미지.
+ *   POST /api/board/images   업로드(로그인 필요) → {url: "/api/images/{id}"}
+ *   GET  /api/images/{id}     이미지 바이트(공개 — img src 로 인증 없이 로드)
+ */
+@RestController
+@RequiredArgsConstructor
+public class BoardImageController {
+
+    private final BoardImageService service;
+
+    @PostMapping("/api/board/images")
+    public Map<String, String> upload(
+            @RequestParam("image") MultipartFile file,
+            @RequestAttribute(AuthInterceptor.CURRENT_MEMBER) SessionUser current) throws IOException {
+        if (file.isEmpty()) {
+            throw new ApiException(HttpStatus.BAD_REQUEST, "이미지가 비어 있습니다.");
+        }
+        String contentType = file.getContentType();
+        if (contentType == null || !contentType.startsWith("image/")) {
+            throw new ApiException(HttpStatus.BAD_REQUEST, "이미지 파일만 업로드할 수 있습니다.");
+        }
+        Long id = service.save(current.getId(), contentType, file.getBytes());
+        return Map.of("url", "/api/images/" + id);
+    }
+
+    @GetMapping("/api/images/{id}")
+    public ResponseEntity<byte[]> get(@PathVariable Long id) {
+        BoardImage img = service.get(id);
+        if (img == null) {
+            return ResponseEntity.notFound().build();
+        }
+        return ResponseEntity.ok()
+                .contentType(MediaType.parseMediaType(img.getContentType()))
+                .cacheControl(CacheControl.maxAge(365, TimeUnit.DAYS).cachePublic())
+                .body(img.getData());
+    }
+}