Published-internal compatibility shim.
Identity and derivation implementation ownership moved into `uselesskey-core`.
Existing imports from this crate remain available during the compatibility-shim
period:
```rust
use uselesskey_core_id::{ArtifactId, DerivationVersion, Seed};
```
Prefer `uselesskey-core` for supported extension work. The canonical identity
implementation now lives at `uselesskey_core::srp::identity`.