feat(#139): add TTL auto-renewal for active users

[kimmoris12345]

Closes #139

Summary

Adds TTL auto-renewal for active users so that their metadata keys (WrapCount, LatestPeriod) stay alive when they mint new wraps. Historical wrap records are not auto-renewed — that requires period enumeration (Issue #90).

Changes

src/lib.rs

• renew_all_ttls(user) (line 457): New admin-only function that extends TTL for WrapCount, LatestPeriod, and the contract instance. Documents dependency on Issue feat: Add multi-period wrap summary query (aggregate stats across months) #90 for full wrap enumeration.
• extend_ttl doc comment (line 383): Comprehensive TTL lifecycle documentation covering automatic metadata renewal, manual wrap renewal, admin bulk renewal, and expiry risk.

src/test.rs — 5 new tests (line 1291)

Test	Purpose
test_metadata_ttl_extended_on_new_mint	Verifies WrapCount and LatestPeriod survive across multiple mints
test_old_wrap_preserved_on_new_mint	Verifies old wraps are not corrupted/lost on new mint (not auto-extended)
test_renew_all_ttls_extends_metadata	Verifies admin bulk-renewal works
test_renew_all_ttls_requires_admin_auth	Verifies admin auth required
test_renew_all_ttls_before_init_fails	Verifies fail before init

SECURITY_RECOMMENDATIONS.md

• Added "TTL Lifecycle & Data Freshness" section with:
  • TTL strategy table per storage key
  • Design decision rationale (auto-renew metadata only)
  • Mitigation recommendations (off-chain bots, admin bulk renewal)
  • Gas analysis cost estimates
  • Test coverage table

Design Decision

Auto-renew metadata only — WrapCount and LatestPeriod were already being extended on every mint_wrap. This PR documents that behavior and adds renew_all_ttls for admin bulk metadata renewal. Historical wraps are not auto-renewed because period enumeration (Issue #90) is required to iterate them on-chain.

Verification

All 54 tests pass (cargo test).

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