feat: production branch with deploy config for baota panel

- Add deploy/ directory with production env, supervisor, nginx, migration configs
- Include all latest features: admin management, feedback, footer with ICP/beian
- Database: foreign_trade (PostgreSQL), user: foreign_trade
- Frontend: trade.yuzhiran.com, backend proxy via Nginx

backend/app/models/system_config.py

@@ -0,0 +1,15 @@
+from sqlalchemy import Column, String, DateTime, Text
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from datetime import datetime
+from app.database import Base
+import uuid
+
+
+class SystemConfig(Base):
+    __tablename__ = "system_configs"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    key = Column(String(100), unique=True, nullable=False, index=True)
+    value = Column(JSONB, nullable=False, default={})
+    description = Column(Text, default="")
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)