[ci] build-cli: add logins entry for registry.viktorbarzin.me:5050

## Context
The infra CLI image (`viktorbarzin/infra` + `registry.viktorbarzin.me:5050/infra`)
is built by `.woodpecker/build-cli.yml` via plugin-docker-buildx and
pushed to two repos. The private-registry htpasswd auth that went in
on 2026-03-22 (memory 437) was never wired into this pipeline, so the
second push has been failing with `401 Unauthorized` on every blob
HEAD for ~4 weeks. That in turn kept every infra pipeline's overall
status at `failure`, which fooled the service-upgrade agent into
spurious rollbacks before the per-workflow check in bd code-3o3.

Now that the agent ignores overall status, this is purely cosmetic —
but worth fixing so the pipeline list goes green and the private-
registry mirror of the infra CLI image stays fresh.

## This change
Extend the plugin's `logins:` array with an entry for
`registry.viktorbarzin.me:5050`, pulling credentials from two
Woodpecker global secrets `registry_user` / `registry_password`.

Secrets plumbing (no CI config changes needed long-term — already
`vault-woodpecker-sync` compatible):
- Vault `secret/ci/global` now carries `registry_user` +
  `registry_password`, copied from `secret/viktor` via
  `vault kv patch`.
- `vault-woodpecker-sync` CronJob picks them up on next run and
  POSTs them to Woodpecker via the API. Also triggered manually
  as `manual-sync-1776613321` → "Synced 8 global secrets from
  Vault to Woodpecker".
- `curl -H "Authorization: Bearer <wp-api-token>" .../api/secrets`
  now lists both `registry_user` and `registry_password`.

## What is NOT in this change
- A follow-on cleanup of the `docker_username`/`docker_password`
  globals (which are actually DockerHub creds mis-named). They still
  work — renaming would cascade across several older pipelines.
- Restoring inline BuildKit cache — commit 0c123903 disabled
  `cache_from/cache_to` due to registry cache corruption; leaving
  that alone here.

## Test Plan
### Automated
Will be validated by the CI run of this very commit:
- `build-cli` workflow should log `#14 [auth] viktor/registry.viktorbarzin.me:5050` successful
- blob HEAD returns 200/404 instead of 401
- step `build-image` exits 0
- overall pipeline status: success (FINALLY)

### Manual Verification
```
$ curl -sS -H "Authorization: Bearer $(vault kv get -field=woodpecker_api_token secret/ci/global)" \
    https://ci.viktorbarzin.me/api/secrets | jq '.[] | .name' | grep registry
"registry_password"
"registry_user"

$ curl -sSI -u viktor:$PASS https://registry.viktorbarzin.me:5050/v2/infra/manifests/<8-char-sha>
HTTP/2 200
```

Closes: code-12b

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

.woodpecker/build-cli.yml

@@ -23,6 +23,14 @@ steps:
           username: viktorbarzin
           password:
             from_secret: dockerhub-pat
+        # Private registry on :5050 requires htpasswd auth since 2026-03-22.
+        # Without this, buildx pushes the second repo but blob HEAD comes
+        # back 401 → pipeline fails → CI false-negative (see bd code-12b).
+        - registry: registry.viktorbarzin.me:5050
+          username:
+            from_secret: registry_user
+          password:
+            from_secret: registry_password
       dockerfile: cli/Dockerfile
       context: cli
       auto_tag: true