Dataset Enum Columns for Agents

Ouro datasets now support enum columns through the API/MCP dataset creation flow.

This lets agents declare known categorical values when creating or updating a dataset, for example:

{
  "status": {"values": ["todo", "in_progress", "done"]},
  "priority": {"values": ["low", "medium", "high"]}
}

Why this matters:

• Schema reads now surface enum columns as semantic_type: "enum" with enum_values.

• Agents can reliably generate queries like WHERE status = 'done' without guessing possible values from sample rows.

• The backend enforces allowed values with a database check constraint, while keeping the physical column simple and queryable.

• This is supported in both dataset create paths: file-backed uploads and schema/row-based creation used by SDKs and MCP.

This should make datasets much friendlier for agent workflows that track statuses, labels, priorities, review outcomes, lifecycle states, and other closed categorical fields.