fix: Dockerfile에 NEXT_PUBLIC_API_URL ARG 추가, ENV 형식 수정

frontend/Dockerfile

@@ -14,7 +14,10 @@ WORKDIR /app
 COPY --from=deps /app/node_modules ./node_modules
 COPY . .
 
-ENV NEXT_TELEMETRY_DISABLED 1
+# Build-time environment variable for API URL
+ARG NEXT_PUBLIC_API_URL=https://autonetsellcar.com
+ENV NEXT_PUBLIC_API_URL=${NEXT_PUBLIC_API_URL}
+ENV NEXT_TELEMETRY_DISABLED=1
 
 RUN npm run build
 
@@ -22,8 +25,8 @@ RUN npm run build
 FROM base AS runner
 WORKDIR /app
 
-ENV NODE_ENV production
-ENV NEXT_TELEMETRY_DISABLED 1
+ENV NODE_ENV=production
+ENV NEXT_TELEMETRY_DISABLED=1
 
 RUN addgroup --system --gid 1001 nodejs
 RUN adduser --system --uid 1001 nextjs
@@ -40,7 +43,7 @@ USER nextjs
 
 EXPOSE 3000
 
-ENV PORT 3000
-ENV HOSTNAME "0.0.0.0"
+ENV PORT=3000
+ENV HOSTNAME=0.0.0.0
 
 CMD ["node", "server.js"]