Expose voting metrics, power, and rationales consistently

[mesudip]

Outcome

Voting activity, live metrics, voting power, and rationales use consistent semantics across DReps, Governance Actions, and providers.

Scope

• Define calculation rules and provenance for vote metrics
• Define voting-power snapshots and historical semantics
• Normalize vote rationale retrieval and validation state
• Add cross-provider fixtures and 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.