Refactor code structure for improved readability and maintainability

app/models/base.py

@@ -0,0 +1,13 @@
+from datetime import UTC, datetime
+
+from sqlmodel import Field, SQLModel
+
+
+class BaseModel(SQLModel):
+    """Base model with common fields for all models."""
+
+    id: int | None = Field(primary_key=True, default=None)
+
+    # timestamps
+    created_at: datetime = Field(default_factory=lambda: datetime.now(UTC))
+    updated_at: datetime = Field(default_factory=lambda: datetime.now(UTC))