Portainer Dashboard widget: multiple issues

### Widget link

https://github.com/glanceapp/community-widgets/blob/main/widgets/portainer-dashboard/README.md

### Description

- The instructions to obtain a Portainer API key appear to be an AI hallucination. The referenced menu options do not exist.
- Actual instructions: https://docs.portainer.io/api/access

- Incorrect AI-hallucinated API references (so widget always shows `0`) for:
- Networks
- Healthy container count
- (Possibly unhealthy container count, but I have no unhealthy containers to test)

Start with the linked portainer-dashboard README and compare its API-key instructions with Portainer's access documentation. Locate the widget references for Networks and container health counts, then verify the API fields and update the instructions and references so the counts no longer show 0; test unhealthy containers if possible.

Written by the indexing model from the issue text.