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.bash

@@ -188,7 +188,7 @@ _mcpctl() {
             COMPREPLY=($(compgen -W "--type --model --url --tier --description --api-key-ref --extra --force -h --help" -- "$cur"))
             ;;
           secretbackend)
-            COMPREPLY=($(compgen -W "--type --description --default --url --namespace --mount --path-prefix --token-secret --config --force -h --help" -- "$cur"))
+            COMPREPLY=($(compgen -W "--type --description --default --url --namespace --mount --path-prefix --auth --token-secret --role --auth-mount --sa-token-path --config --force -h --help" -- "$cur"))
             ;;
           project)
             COMPREPLY=($(compgen -W "-d --description --proxy-model --prompt --llm --llm-model --gated --no-gated --server --force -h --help" -- "$cur"))