**Motivations:**
- Fix import error when importing nsec private keys
- Support both string and Uint8Array formats from nip19.decode
**Root causes:**
- nip19.decode returns decoded.data as Uint8Array, not string
- Validation in KeyManagementManager only checked for string type
- importPrivateKey in keyManagement.ts only handled string type
**Correctifs:**
- Updated KeyManagementManager validation to accept Uint8Array
- Updated importPrivateKey to convert Uint8Array to hex using bytesToHex
- Improved error messages to show actual validation errors
**Evolutions:**
- None
**Pages affectées:**
- components/KeyManagementManager.tsx
- lib/keyManagement.ts