Function deriveScopeKey

deriveScopeKey(masterKey: Uint8Array, scope: string): Uint8Array
Derives a scope-specific 32-byte key via HKDF-SHA256.
Parameters
- masterKey: Uint8Array
  65-byte master key material from deriveMasterKey.
- scope: string
  Scope identifier (e.g. "instagram.profile").
Returns Uint8Array
32-byte derived key suitable for symmetric encryption.

Remarks
Uses salt="vana" and info="scope:{scope}" per spec §2.3.
- Defined in crypto/keys/derive.ts:78