Expose a per-account historical event query view for off-chain audit and reconciliation

[phertyameen]

Location

contracts/ephemeral_account/src/lib.rs

Problem

While events are emitted per-action, Soroban event retention at the RPC layer is time-limited; no confirmed on-chain view function lets a caller retrieve a summarized history for a specific account (e.g. funded-at, claimed-at, swept-at timestamps) after the underlying raw events may have aged out of RPC-queryable history, relevant for dispute resolution or long-after-the-fact audits.

Acceptance Criteria

• A minimal, storage-efficient historical summary (not full event replay) is retained and queryable per account for at least as long as the account itself persists in storage
• Explicitly scoped to avoid the unbounded-growth risk flagged in the pagination issue, e.g. fixed-size summary rather than an ever-growing log
• Cross-referenced with the previously-proposed AuditLog contract to avoid duplicating functionality unnecessarily