feat: add config show command for active microcks context

Nobody has claimed this yet.

the cli stores microcks connection details in the local config, but there is no simple command that shows what the active context currently points to. when debugging `microcks import`, `microcks test`, or local tooling that connects to microcks, users currently have to inspect the raw config file manually to confirm the current context, server url, tls setting, and whether auth credentials are present.

a `microcks config show` command would make that state visible from the cli without exposing secrets. the default output could print a small table with the current context name, server url, insecure tls setting, whether an auth token is present, whether a refresh token is present, and linked local instance information if the context has one.

example:

```bash
microcks config show
```

```text
current context server insecure tls auth token instance
local http://localhost:8585 false present microcks
```

the first version can stay focused: add a `config show` command under `cmd/`, reuse the existing local config loading and context resolution code, mask token values instead of printing them, add tests with temporary config fixtures, and update command documentation.

this also supports the vs code integration work in #255 because editor tooling needs an easy way for users to confirm which microcks instance their local environment is configured to use.

Start under cmd/ by tracing the existing local config loading and context resolution used by the CLI. Add the config show entry point and inspect the temporary config fixture tests to cover context, server URL, TLS, token presence, refresh-token presence, and linked instance details without printing secrets. Update the command documentation when the output and tests are complete.

Written by the indexing model from the issue text.