Define Governance API v1

## Outcome

A stable provider-independent Governance API contract defines canonical governance data, pagination, freshness, capabilities, and errors.

## Scope

- Define canonical domain types and endpoint contracts
- Define provider capability and health semantics
- Define pagination, freshness, live-data, and degraded-mode behavior
- Publish an implementation guide and provider contract-test suite

## 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.