Kaapi v1.0: DB comments #475

Is your feature request related to a problem?

Our database schema has no column comments. This leads to confusion for non-developers (though we have a description in the API), but just looking at the database time is wasted figuring out column's purpose

Describe the solution you'd like
Add comments to database columns, especially for:

• Columns with non-obvious purposes
• Status/type fields (document what valid values mean)
• JSON/metadata columns (describe expected structure)
• Foreign keys (clarify the relationship)