Implement the Blockfrost governance data provider

[mesudip]

Outcome

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

Scope

• Confirm the Blockfrost capability matrix
• Implement canonical mappings and provider errors
• Handle authentication, rate limits, retries, and pagination
• 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 sample modernization epic. Its child features and tasks will be added after the board structure is reviewed.