Add Pen model

models/pen.py

@@ -0,0 +1,17 @@
+from sqlalchemy import Column, String, Integer, Boolean, DateTime, ForeignKey
+from sqlalchemy.sql import func
+from core.database import Base
+import uuid
+
+class Pen(Base):
+    __tablename__ = "pens"
+    
+    id = Column(String, primary_key=True, default=lambda: str(uuid.uuid4()))
+    name = Column(String, nullable=False)
+    brand = Column(String, nullable=False)
+    color = Column(String, nullable=False)
+    price = Column(Integer, nullable=False)
+    in_stock = Column(Boolean, default=True)
+    description = Column(String)
+    created_at = Column(DateTime, default=func.now())
+    updated_at = Column(DateTime, default=func.now(), onupdate=func.now())