Update Arbeitsagentur API Integration for Current V6 and V4 Response Schemas

Arbeitsagentur Jobsuche API differs from the official OpenAPI documentation and the current integration.

## Observed behaviour

Endpoint `GET /pc/v6/jobs` does return key
```
{
ergebnisliste: []
}
```

## Expected

from documentation to return a key `stellenangebote` but this is missing

Also i detected difference in other fields as well:

| Documented | Actual |
|---|---|
| `stellenangebote` | `ergebnisliste` |
| `refnr` | `referenznummer` |
| `titel` | `stellenangebotsTitel` |
| `arbeitgeber` | `firma` |
| `aktuelleVeroeffentlichungsdatum` | `datumErsteVeroeffentlichung` |
| `arbeitsort` | `stellenlokationen` |
| `modifikationsTimestamp` | `aenderungsdatum` |

The V4 detail endpoint is available and returns `HTTP 200`:

```text
GET /pc/v4/jobdetails/{base64(refnr)}
```

However, it also uses different field names:

| Documented | Actual |
|---|---|
| `titel` | `stellenangebotsTitel` |
| `refnr` | `referenznummer` |
| `arbeitsorte` | `stellenlokationen` |
| `aktuelleVeroeffentlichungsdatum` | `datumErsteVeroeffentlichung` |
| `modifikationsTimestamp` | `aenderungsdatum` |
| `stellenbeschreibung` | `stellenangebotsBeschreibung` |

Expected Behaviour:
- Documentation and actual api follow same structure & schema

Start by inspecting the integration paths for GET /pc/v6/jobs and GET /pc/v4/jobdetails/{base64(refnr)}, then compare their response mappings with the documented schemas. Done means both endpoints are represented consistently using the actual field names listed, and the documentation matches the returned structures.

Written by the indexing model from the issue text.