요청 스코프 언어 컨텍스트와 인터셉터 추가

- Interceptor에서 Accept-Language 헤더를 파싱
- 요청 단위 LangContext에 언어 정보 저장
- 서비스 및 예외 처리 계층에서 언어 컨텍스트 주입
- enum 및 when 기반 언어 정책을 한 곳으로 통합

src/main/kotlin/kr/co/vividnext/sodalive/configs/WebConfig.kt

@@ -1,11 +1,19 @@
 package kr.co.vividnext.sodalive.configs
 
+import kr.co.vividnext.sodalive.i18n.LangInterceptor
 import org.springframework.context.annotation.Configuration
 import org.springframework.web.servlet.config.annotation.CorsRegistry
+import org.springframework.web.servlet.config.annotation.InterceptorRegistry
 import org.springframework.web.servlet.config.annotation.WebMvcConfigurer
 
 @Configuration
-class WebConfig : WebMvcConfigurer {
+class WebConfig(
+    private val langInterceptor: LangInterceptor
+) : WebMvcConfigurer {
+    override fun addInterceptors(registry: InterceptorRegistry) {
+        registry.addInterceptor(langInterceptor).addPathPatterns("/**")
+    }
+
     override fun addCorsMappings(registry: CorsRegistry) {
         registry.addMapping("/**")
             .allowedOrigins(

src/main/kotlin/kr/co/vividnext/sodalive/i18n/Lang.kt

@@ -0,0 +1,22 @@
+package kr.co.vividnext.sodalive.i18n
+
+import java.util.Locale
+
+enum class Lang(val code: String, val locale: Locale) {
+    KO("ko", Locale.KOREAN),
+    EN("en", Locale.ENGLISH),
+    JA("ja", Locale.JAPANESE);
+
+    companion object {
+        fun fromAcceptLanguage(header: String?): Lang {
+            if (header.isNullOrBlank()) return KO
+            val two = header.trim().lowercase().take(2) // 앱은 2자리만 보내지만 안전하게 처리
+            return when (two) {
+                "ko" -> KO
+                "en" -> EN
+                "ja" -> JA
+                else -> KO
+            }
+        }
+    }
+}

src/main/kotlin/kr/co/vividnext/sodalive/i18n/LangContext.kt

@@ -0,0 +1,15 @@
+package kr.co.vividnext.sodalive.i18n
+
+import org.springframework.stereotype.Component
+import org.springframework.web.context.annotation.RequestScope
+
+@Component
+@RequestScope
+class LangContext {
+    var lang: Lang = Lang.KO
+        internal set
+
+    fun setLang(lang: Lang) {
+        this.lang = lang
+    }
+}

src/main/kotlin/kr/co/vividnext/sodalive/i18n/LangInterceptor.kt

@@ -0,0 +1,21 @@
+package kr.co.vividnext.sodalive.i18n
+
+import org.springframework.stereotype.Component
+import org.springframework.web.servlet.HandlerInterceptor
+import javax.servlet.http.HttpServletRequest
+import javax.servlet.http.HttpServletResponse
+
+@Component
+class LangInterceptor(
+    private val langContext: LangContext
+) : HandlerInterceptor {
+    override fun preHandle(
+        request: HttpServletRequest,
+        response: HttpServletResponse,
+        handler: Any
+    ): Boolean {
+        val acceptLanguage = request.getHeader("Accept-Language")
+        langContext.setLang(Lang.fromAcceptLanguage(acceptLanguage))
+        return true
+    }
+}