feat(rpc): add getEpochSchedule

[aspnxdd]

Problem

Superbank does not expose Solana-compatible getEpochSchedule.

Solution

Return the default Solana epoch schedule through JSON-RPC.

Scope

• Add getEpochSchedule handler and dispatch.
• Reject unexpected params.
• Cover handler and router tests.

[Mctursh]

This is a duplicate of #36.