Namespace-prefixed sequences aren't supported

When users define sequences that include the namespace, e.g.

```yaml

sequences:
my-sequence:
actions: >-
namespace/auth,
namespace/real-action
```

They get an error:

```shell
› Sequence component 'namespace/real-action' does not exist (sequence =
› 'my-sequence')
```

This is because in the plugin, we track the action in the sequence as `namespace/auth` for example

But the list of actions we get from the config library tracks actions only in name, e.g. `auth`

Namespace-prefixed actions in a sequence are a valid Runtime use case that we should look into supporting

Start by tracing how the plugin parses sequence actions and compares them with the action names returned by the config library. Reproduce the namespace-prefixed sequence from the issue, then verify that `namespace/auth` and `namespace/real-action` resolve successfully while unprefixed sequences continue to work.

Written by the indexing model from the issue text.