fix(P07): remove all password/token paths (REQ-146, R-021, C-34) -- BREAKING

---ci---
project: orca
phase: 7
milestone: v0.12
status: execute
---/ci---

R-021 invariant: no passwords, no Orca-issued tokens, no CA-key
passphrases anywhere in the system.

Removed:
- proxmox/bootstrap.go: ssh.Password auth -> ssh.PublicKeys (key-based).
  --password/ removed from node join; replaced
  with --ssh-key (default: orca SSH key). Pre-staged key required.
- stepca/stepca.go: --password-file /dev/stdin removed from Init and
  issueCert. Provisioner changed to 'orca-oidc' (OIDC provisioner).
- identity/spiffe.go: --password-file removed from MintSVID. Provisioner
  changed to 'orca-oidc'.

Tests: all proxmox, stepca, identity, cli tests updated + pass. 3 new
password-rejection regression tests. Fake SSH server gains
PublicKeyCallback. go vet clean. Full build green.

internal/proxmox/bootstrap.go

@@ -61,9 +61,11 @@ type Options struct {
 	Host string
 	// SSHUser is the initial SSH username (default "root").
 	SSHUser string
-	// Password is the SSH password for the initial connection.
-	// NEVER persisted (D-031). The caller must zero this after use.
-	Password string
+	// SSHKeyPath is the path to the private SSH key for key-based auth
+	// (R-021: no passwords). The operator pre-stages the orca SSH public
+	// key on the remote host out-of-band (or uses step ssh for an
+	// OIDC-issued cert). Required.
+	SSHKeyPath string
 	// ProxmoxUser is the Linux system user to create on the host
 	// (default "orca"). Config-overridable.
 	ProxmoxUser string
@@ -101,8 +103,8 @@ func BootstrapProxmox(ctx context.Context, opts Options) (*Result, error) {
 	if opts.Host == "" {
 		return nil, fmt.Errorf("proxmox bootstrap: host is required")
 	}
-	if opts.Password == "" {
-		return nil, fmt.Errorf("proxmox bootstrap: password is required (use --password or $ORCA_PROXMOX_PASSWORD)")
+	if opts.SSHKeyPath == "" {
+		return nil, fmt.Errorf("proxmox bootstrap: SSH key path is required (R-021: no passwords; pre-stage the orca SSH key or use step ssh)")
 	}
 	if opts.SSHUser == "" {
 		opts.SSHUser = "root"
@@ -152,9 +154,18 @@ func BootstrapProxmox(ctx context.Context, opts Options) (*Result, error) {
 		hostKeyCallback = cb
 	}
 
+	// Load the SSH private key for key-based auth (R-021: no passwords).
+	keyBytes, err := os.ReadFile(opts.SSHKeyPath)
+	if err != nil {
+		return nil, fmt.Errorf("read SSH key %s: %w", opts.SSHKeyPath, err)
+	}
+	signer, err := ssh.ParsePrivateKey(keyBytes)
+	if err != nil {
+		return nil, fmt.Errorf("parse SSH key %s: %w", opts.SSHKeyPath, err)
+	}
 	sshConfig := &ssh.ClientConfig{
 		User:            opts.SSHUser,
-		Auth:            []ssh.AuthMethod{ssh.Password(opts.Password)},
+		Auth:            []ssh.AuthMethod{ssh.PublicKeys(signer)},
 		HostKeyCallback: hostKeyCallback,
 		Timeout:         10 * time.Second,
 	}