feat(settings): add SMTP admin configuration

backend/hermes/app/models/system_setting.py

@@ -0,0 +1,21 @@
+from datetime import datetime
+
+from sqlalchemy import Boolean, DateTime, String, Text, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.database import Base
+
+
+class SystemSetting(Base):
+    __tablename__ = "system_settings"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    key: Mapped[str] = mapped_column(String(160), unique=True, index=True)
+    value: Mapped[str] = mapped_column(Text, default="", server_default="")
+    is_secret: Mapped[bool] = mapped_column(Boolean, default=False, server_default="false")
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+        onupdate=func.now(),
+    )