feat: activity log model + API (audit trail)

app/main.py

@@ -253,6 +253,7 @@ def startup():
     from app.core.config import Base, engine
     from app.models import webhook
     from app.models import apikey
+    from app.models import activity
     Base.metadata.create_all(bind=engine)
 
 
@@ -649,3 +650,46 @@ def batch_assign(data: BatchAssign, db: Session = Depends(get_db)):
     db.commit()
     
     return {"updated": len(updated), "issue_ids": updated, "assignee_id": data.assignee_id}
+
+
+
+# ============ Activity Log ============
+
+from app.models.activity import ActivityLog
+
+
+class ActivityLogResponse(PydanticBaseModel):
+    id: int
+    action: str
+    entity_type: str
+    entity_id: int
+    user_id: int | None
+    details: str | None
+    created_at: datetime
+    class Config:
+        from_attributes = True
+
+
+def log_activity(db: Session, action: str, entity_type: str, entity_id: int, user_id: int = None, details: str = None):
+    """Helper to record an activity log entry."""
+    entry = ActivityLog(action=action, entity_type=entity_type, entity_id=entity_id, user_id=user_id, details=details)
+    db.add(entry)
+    db.commit()
+
+
+@app.get("/activity", response_model=List[ActivityLogResponse])
+def list_activity(
+    entity_type: str = None,
+    entity_id: int = None,
+    user_id: int = None,
+    limit: int = 50,
+    db: Session = Depends(get_db)
+):
+    query = db.query(ActivityLog)
+    if entity_type:
+        query = query.filter(ActivityLog.entity_type == entity_type)
+    if entity_id:
+        query = query.filter(ActivityLog.entity_id == entity_id)
+    if user_id:
+        query = query.filter(ActivityLog.user_id == user_id)
+    return query.order_by(ActivityLog.created_at.desc()).limit(limit).all()