Breitbandmessung: Internetprovider und Tarife (Bundesnetzagentur)

# Providerliste

```
curl https://breitbandmessung.de/api/provider
```

Returns:
```json
[{
"key": "927",
"operator": "489",
"company": "Stadtwerke Velbert GmbH\/.comBERT",
"value": ".comBERT \/ Stadtwerke Velbert",
"istop": 0,
"hasPlans": 1
}, {
"key": "1",
"operator": "1",
"company": "1&1",
"value": "1&1",
"istop": 1,
"hasPlans": 1
}, {
…
```

# Tarifliste
```
curl https://breitbandmessung.de/api/plans_desktop/{PROVIDER_ID}
```

Returns
```json
[{
"key": "99319",
"value": "Basic 50",
"mindownload": "16700",
"normdownload": "44000",
"maxdownload": "50000",
"maxdownloadpub": "50000",
"minupload": "1600",
"normupload": "9600",
"maxupload": "10000",
"plan_id": "99319",
"plan_db_version": "291"
}, {
"key": "99317",
"value": "Business-Flat 100",
"mindownload": "54000",
"normdownload": "88600",
"maxdownload": "100000",
"maxdownloadpub": "100000",
"minupload": "20000",
"normupload": "36900",
"maxupload": "40000",
"plan_id": "99317",
"plan_db_version": "291"
}, {
…
```

Start by querying the mentioned provider endpoint and a provider-specific plans_desktop endpoint to inspect the available fields and identifiers. The issue does not name repository files, tests, or the intended change, so clarify where this data should be integrated and what a complete result should look like before implementation.

Written by the indexing model from the issue text.