feat(contract): version events for transfer, escrow, and admin lifecycle

[arisu6804]

Problem

Indexers cannot reliably reconstruct transfer state when event fields and units change without versioning.

Objective

Deliver a production-quality improvement to contract events and downstream indexers that creates measurable value for correctness, security, reliability, performance, or maintainability.

Implementation scope

• Define explicit versioned schemas including transfer ID, actor, currency, amount, escrow status, timestamps, and outcomes.

Acceptance criteria

• Every lifecycle event is parseable, versioned, and unit-explicit; fixture parsers detect breaking changes.

Required validation

• Event fixtures, compatibility, parser, and end-to-end emission tests.
• Existing tests and CI remain passing.
• Add regression coverage for the original failure mode.
• Do not weaken, delete, or skip unrelated tests to obtain a green build.

PR quality bar

• Keep the PR focused and explain design tradeoffs, compatibility impact, and test evidence.
• Avoid typo-only, documentation-only, cosmetic-only, or unrelated refactor submissions.

Out of scope

• Broad rewrites not required by the acceptance criteria.
• Changes to unrelated services, contracts, or user flows.