Move Roboflow API key to environment variable

- Change hardcoded API key to os.getenv("ROBOFLOW_API_KEY")
- Improves security by using Hugging Face Secrets
- Code can be public while keeping API key private

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app.py

@@ -97,7 +97,8 @@ def detect_with_yolo(image, confidence=0.1):
 # ============================================================
 # Roboflow SDK 설정 (최적화된 방식)
 # ============================================================
-ROBOFLOW_API_KEY = "azcIL8KDJVJMYrsERzI7"
+# 환경변수에서 API 키 읽기 (Hugging Face Secrets 사용)
+ROBOFLOW_API_KEY = os.getenv("ROBOFLOW_API_KEY", "")
 
 # Roboflow Inference SDK 클라이언트 (connection pooling 지원)
 roboflow_client = InferenceHTTPClient(