feat(platform): add audit logs and activity feed

backend/hermes/app/models/audit.py

@@ -0,0 +1,28 @@
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, Integer, JSON, String, Text, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.database import Base
+
+
+class AuditLog(Base):
+    __tablename__ = "audit_logs"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    actor_user_id: Mapped[int | None] = mapped_column(
+        ForeignKey("users.id", ondelete="SET NULL"),
+        nullable=True,
+        index=True,
+    )
+    actor_username: Mapped[str] = mapped_column(String(120), default="", server_default="")
+    action: Mapped[str] = mapped_column(String(120), index=True)
+    entity_type: Mapped[str] = mapped_column(String(80), index=True)
+    entity_id: Mapped[int | None] = mapped_column(Integer, nullable=True, index=True)
+    entity_label: Mapped[str] = mapped_column(String(255), default="", server_default="")
+    ip_address: Mapped[str] = mapped_column(String(80), default="", server_default="")
+    user_agent: Mapped[str] = mapped_column(Text, default="", server_default="")
+    before_data: Mapped[dict | list | None] = mapped_column(JSON, nullable=True)
+    after_data: Mapped[dict | list | None] = mapped_column(JSON, nullable=True)
+    metadata_data: Mapped[dict | list | None] = mapped_column("metadata", JSON, nullable=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())