fix(identity-wallet): address code review feedback for Phase 3
- Import ordering: move 'crypto' import before 'serde' (alphabetical)
- Add HTTP status code logging for GET /v1/relay/keys non-success path
- Add HTTP status code logging for POST /v1/dids non-success path
- Apply rustfmt canonical formatting to method chains
All formatting now passes 'cargo fmt --all --check'.
All 8 DID ceremony serialization tests pass.
Crate builds without warnings (clippy clean).