Migrate `wraith-names` to persistent() storage everywhere

[truthixify]

Tier: M (2-4 days) Type: refactor

Context

PR #35's registry audit moved stealth-registry to persistent storage for scalability. wraith-names still uses instance storage in places, which has the same scaling concern. Audit + migrate.

Scope

• Audit every env.storage().instance() call in wraith-names
• For each, determine: stay instance (small fixed metadata) or migrate to persistent (per-name data)
• Migration is breaking if data is already deployed; coordinate with deploy story
• Update TTL extension logic from the keeper service (Soroban TTL keeper service for wraith-names #50 in this wave) to match

Acceptance criteria

• Storage decisions documented in wraith-names/STORAGE.md
• Migration tests pass
• TTL keeper updated to extend correct storage tier
• Deploy script updated for fresh-deploy path

Files to start with

• stellar/wraith-names/src/lib.rs
• stellar/stealth-registry/src/lib.rs (persistent storage reference)