Implement the Kupo governance data provider

## Outcome

The Governance API can use Kupo for the supported governance-data capability set.

## Scope

- Confirm the Kupo capability matrix
- Implement canonical mappings and provider errors
- Define interaction with complementary providers where Kupo lacks data
- Pass applicable provider contract tests

## Acceptance criteria

- [ ] Scope is decomposed into independently deliverable child issues.
- [ ] Architecture and API decisions are linked from this issue.
- [ ] Test, documentation, observability, rollout, and failure behavior are defined where applicable.
- [ ] Epic exit criteria are verified before closure.

## Planning note

This is a 2026 GovTool revamp work item. Its child features and tasks should be added as the scope is refined.

No files, tests, or entry points are identified. Start by decomposing the Kupo capability matrix and linking the required architecture and API decisions; define provider interactions, contract tests, documentation, observability, rollout, and failure behavior. Done means the child issues exist and the epic exit criteria are verified.

Written by the indexing model from the issue text.