Feed "Der Spiegel" not shown all in arcticle

IMPORTANT

Read and tick the following checkbox after you have created the issue or place an x inside the brackets ;)

• I have read the CONTRIBUTING.md and followed the provided tips
• I accept that the issue will be closed without comment if I do not check here
• I accept that the issue will be closed without comment if I do not fill out all items in the issue template.

Explain the Problem

Comparing article from web and news app, there is something missing:

• most of the time "teaser" is missing
• sometimes the first paragraph of the full text is missing

Steps to Reproduce

Explain what you did to encounter the issue

1. use http://www.spiegel.de/schlagzeilen/index.rss
2. enable full text
3. see a difference between web and news article

System Information

• News app version: 24.0.0
• Nextcloud version: 30.0.2.2
• Cron type: system cron
• PHP version: 8.3.2
• Database and version: mariadb
• Browser and version: Firefox and Android app
• OS and version: Linux

Start by reproducing the issue with http://www.spiegel.de/schlagzeilen/index.rss and the full-text option enabled, comparing the News article with the web version. Trace the feed article extraction and full-text handling, then verify that the teaser and first paragraph are preserved in the resulting article.