Improve Governance Action context and activity APIs

## Outcome

Governance Actions include the context and activity needed to understand their lifecycle and participation.

## Scope

- Define Governance Action context and activity models
- Expose lifecycle events, voting activity, past votes, and rationales
- Include live vote metrics and relevant voting-power context
- Define consistency and freshness expectations across providers

## 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.

Start by decomposing the context and activity scope into independently deliverable child issues. Define the architecture and API decisions, then identify applicable test, documentation, observability, rollout, and failure-behavior work. The epic is done when the child scope is delivered and its exit criteria are verified.

Written by the indexing model from the issue text.