nebula-mesh: Decrypted CA private key persists in heap after signing
internal/pki/resolver.go:36-64 constructs a CAManager with the plaintext ed25519.PrivateKey after unwrapping via the master key; internal/pki/ca.go:13-16 stores it. Callers at internal/api/enroll.go:116, internal/api/updates.go:297, and internal/api/mobile_bundle.go:40 use the manager for one Sign() and drop the reference on function return — but the underlying slice contents are not wiped before release. The keystore package's contract (internal/keystore/keystore.go doc: "Callers MUST zeroise the returned plaintext DEK as soon as it is no longer needed") is not …