feat(openbao): kubernetes ServiceAccount auth — no static token in DB

Why: requiring a static OpenBao root token to live (even once-bootstrap) on
the plaintext backend is the weakest link in the chain. With the bao-side
Kubernetes auth method enabled, mcpd's pod can authenticate using its own
projected SA token, exchange it for a short-lived Vault client token, and
keep the database free of any vault credentials at all.

Driver changes (src/mcpd/src/services/secret-backends/openbao.ts):
- New `OpenBaoConfig.auth = 'token' | 'kubernetes'`. Defaults to 'token' so
  existing rows keep working. Both shapes share url + mount + pathPrefix +
  namespace; auth-specific fields are mutually exclusive in the config schema.
- Kubernetes auth flow: read JWT from /var/run/secrets/.../token, POST to
  /v1/auth/<authMount>/login {role, jwt}, cache the returned client_token
  for `lease_duration - 60s` (grace window), then re-login.
- One-shot 403-retry: if a request comes back 403 (revoked / clock skew),
  purge cache and retry the original request once with a fresh login.
- Reads + writes go through the same getToken() path so token-auth is
  unchanged for existing deployments.

CLI (src/cli/src/commands/create.ts):
- `mcpctl create secretbackend bao --type openbao --auth kubernetes \
     --url https://bao.example:8200 --role mcpctl`
- Optional `--auth-mount` (default 'kubernetes') + `--sa-token-path` (default
  the standard projected-token path) for non-default deployments.
- Token-auth path unchanged: `--auth token --token-secret SECRET/KEY`
  (or omit `--auth` since 'token' is the default).

Validation (factory.ts) gates on the auth strategy: each path enforces its
own required fields and produces a clear error if misconfigured.

Tests: 6 new k8s-auth unit cases (login wire shape, lease-based caching,
custom authMount, 403-on-login, missing-role rejection, missing-tokenSecretRef
rejection). Full suite 1859/1859. Completions regenerated for the new flags.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

completions/mcpctl.fish

@@ -336,7 +336,11 @@ complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l url -d 'o
 complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l namespace -d 'openbao: X-Vault-Namespace header value' -x
 complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l mount -d 'openbao: KV v2 mount point (default: secret)' -x
 complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l path-prefix -d 'openbao: path prefix under mount (default: mcpctl)' -x
-complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l token-secret -d 'openbao: token secret reference in SECRET/KEY form (e.g. bao-creds/token)' -x
+complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l auth -d 'openbao: auth method — \'token\' (default) or \'kubernetes\'' -x
+complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l token-secret -d 'openbao token auth: token secret reference in SECRET/KEY form (e.g. bao-creds/token)' -x
+complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l role -d 'openbao kubernetes auth: vault role to login as (e.g. \'mcpctl\')' -x
+complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l auth-mount -d 'openbao kubernetes auth: vault auth method mount path (default: \'kubernetes\')' -x
+complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l sa-token-path -d 'openbao kubernetes auth: filesystem path to projected SA token (default: \'/var/run/secrets/kubernetes.io/serviceaccount/token\')' -x
 complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l config -d 'Extra config as key=value (repeat for multiple)' -x
 complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l force -d 'Update if already exists'