perf(contract): define TTL policy for transfers, callers, and admin state

[arisu6804]

Problem

Unclear storage expiry can remove active transfers or cause redundant writes and budget failures.

Objective

Deliver a production-quality improvement to persistent storage and TTL bumps that creates measurable value for correctness, security, reliability, performance, or maintainability.

Implementation scope

• Define TTL classes, avoid repeated bumps, and add bounded cleanup for terminal records only.

Acceptance criteria

• Live records remain available within policy; cleanup cannot remove active escrow; storage operations stay within budget.

Required validation

• Instrumentation, expiry, cleanup, and transaction-budget 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.