feat(core): implement AuthContext, Identity, AuthToken, IdentityProvider, ConfigIdentityProvider (task: core/auth)
Implement authentication types in auth.rs: AuthContext (Clone, 4 fields),
Identity (Clone, PartialEq), AuthToken, IdentityProvider trait (resolve_from_
fingerprint + resolve_from_token), ConfigIdentityProvider (reads from
ArcSwap<DynamicConfig> on every call — hot-reloadable). Fingerprint resolution
via authorized_fingerprints HashSet, token resolution via alk_ prefix + SHA-256
hash + expiry check. Also implemented minimal config.rs types (DynamicConfig,
AuthPolicy, ApiKeyEntry, RateLimitConfig, ConfigReloadHandle) needed by auth —
aligned with architecture docs for the parallel core/config task to extend.
27 unit tests pass; clippy clean.
Refs: docs/architecture/crates/core/auth.md
Implements: ADR-004, ADR-011
glm-5.2
a4b4d89d8f