Returns comprehensive metadata for a single key including:

• Lifecycle information (status, created/expires timestamps)
• Usage tracking (usage count, limits)
• Algorithm details (kty, alg)
• Capability flags (exportable, origin, restricted, keyOps)
• Integrity verification (hash/fingerprint)

This endpoint is suitable for administrative dashboards, key inventory
systems, and compliance audits where cryptographic material exposure
is unnecessary.

Note: To retrieve the public key material, use the migration endpoint
GET /api/migration/keys/{kid} which enforces exportable flag validation.