feat(secrets): opt-in injected secret delivery, scoped per server

Completes the path that stops mcpd writing secret VALUES into MCP server
pod specs. With `secretDelivery: injector`, the pod fetches its own
secrets from OpenBao through the agent injector, under a ServiceAccount
and role scoped to just that server's secrets — so the value never enters
etcd, and gitea-mcp cannot read the Grafana token.

Opt-in per server, defaulting to `env`. Every existing server is
bit-for-bit unchanged, and migrating is one reversible decision at a time
rather than a flag day.

The two invariants under most risk, both tested:

- **Opted-out servers produce an identical manifest.** No annotations, no
  serviceAccountName, automountServiceAccountToken still false.

- **Opted-in servers still fail LOUDLY on a bad ref.** Once mcpd stops
  reading a server's secrets, the check e6cd735 added no longer fires for
  it, and a typo'd secretRef would degrade into a vault-agent-init
  crashloop that mcpd reports as a generic pod failure — the same class of
  bug that had gitea-mcp running for weeks on an empty token while
  reporting healthy. `validateServerEnvRefs` resolves every ref and throws
  the value away, purely to keep that error. After the value cache it is a
  cache hit and costs nothing.

Shell quoting is the other silent-failure trap and is treated as part of
the contract: the agent renders `export NAME='value'` and the container
command sources it, so a value containing a space, `$`, a quote or a
newline would truncate and yield an empty token. `shellSingleQuote` is
tested by executing a real /bin/sh over nine adversarial values including
`'; export PWNED=1; '` — and those tests fail against naive quoting,
confirmed before keeping them.

`sh -c <script> arg0 arg1 …` preserves argv via $0/$@, and `exec` keeps
PID 1 as the real process, which matters because mcpd attaches to PID 1's
stdin/stdout for STDIO servers.

Docker/Podman declare `capabilities.secretRefs: false` and fall back to
inline resolution, so local development is untouched. Deleting a server
revokes its identity, after its pods are gone and best-effort — a role no
pod can authenticate as grants nothing, and failing the delete over it
would strand the row.

Per the CLI rules, `secretDelivery`/`entrypoint` are `create` flags,
round-trip through apply -f, and show in `describe server` — which now
also flags servers still inlining secrets into their pod spec.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018vybEitX4FykeMatKe5Xki

completions/mcpctl.bash

@@ -194,7 +194,7 @@ _mcpctl() {
       else
         case "$create_sub" in
           server)
-            COMPREPLY=($(compgen -W "-d --description --package-name --runtime --docker-image --transport --repository-url --external-url --command --container-port --replicas --env --volume --health-check-tool --health-check-args --health-check-interval --health-check-timeout --health-check-failure-threshold --from-template --env-from-secret --force -h --help" -- "$cur"))
+            COMPREPLY=($(compgen -W "-d --description --package-name --runtime --docker-image --transport --repository-url --external-url --command --container-port --replicas --env --volume --health-check-tool --health-check-args --health-check-interval --health-check-timeout --health-check-failure-threshold --secret-delivery --entrypoint --from-template --env-from-secret --force -h --help" -- "$cur"))
             ;;
           secret)
             COMPREPLY=($(compgen -W "--data --force -h --help" -- "$cur"))