nebula-mesh: CA private key not zeroized on web mobile-bundle error paths

Impact The web handler renderMobileBundle internal/web/handlers.go:1325 passes the real pki.CAResolver directly into mobilebundle.Build. Inside Build internal/mobilebundle/builder.go:54, resolver.LoadByID decrypts the CA's ed25519 private key into a pki.CAManager, but Build never calls...

GHSA-8H84-FHQQ-Q58V 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/mobilebundle.go:40 use the manager for one Sign...