magnet links get interpreted as relative links

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Explain the Problem

What problem did you encounter?
Feeds that contain magnet links (as the example feed below) get parsed as relative links of the form https://www.website.commagnet/?xt=urn:btih:343434343434343434&dn=Example.File.Name%5D&tr=udp://tracker.opentrackr.org/announce and are therefore not valid links.

Steps to Reproduce

Explain what you did to encounter the issue

1. Add any feed with magnet links
2. Links of title are malformed.
3. Clicking on them causes browser to load new tab which fails to reach anything instead of handing over to the designated magnet: link handler

System Information

• News app version: 28.6.0 (bug present going a long time back, so it's not a recent regression)
• Nextcloud version: 34.0.1
• Cron type: (system cron/python updater/...) system
• PHP version: 8.3.6
• Database and version: mysql 10.11.14
• Browser and version: Firefox 152.0
• OS and version: Fedora Linux 44

Example feed (which would produce the above link):

<rss version="2.0">
           <channel>
              <title>Example feed</title>
              <link>https://www.website.com</link>
              <ttl>300</ttl>
              <description>An example of a feed that breaks News parsing</description>
		<item>
                        <title>Example File name</title>
                        <link>magnet:?xt=urn:btih:343434343434343434&amp;dn=Example.File.Name&amp;tr=udp%3A%2F%2F47tracker.opentrackr.org%3A6969%2Fannounce</link>
                        <guid isPermaLink="false">3d6e18b985be345454545454545454545</guid>
                        <pubDate>Mon, 25 May 2026 06:53:52 +0000</pubDate>
                        <description>New File: Example File</description>
                        <enclosure url="magnet:?xt=urn:btih:343434343434343434&amp;dn=Example.File.Name&amp;tr==udp%3A%2F%2Ftracker.opentracker.org%3A6969%2Fannounce" length="0" type="application/x-bittorrent"/>
                     </item>
...

{"reqId":"xeiECrRrFMbwIM70i4iP","level":2,"time":"2026-07-15T13:23:59+00:00","remoteAddr":"XX.XX.XX.XX","user":"--","app":"PHP","method":"GET","url":"/ocs/v2.php/core/update?requesttoken=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx","scriptName":"/ocs/v2.php","message":"Cannot modify header information - headers already sent by (output started at /var/www/nextcloud/lib/private/EventSource.php:60) at /var/www/nextcloud/lib/private/AppFramework/Http/Output.php#49","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:152.0) Gecko/20100101 Firefox/152.0","version":"34.0.1.2","data":{"app":"PHP"}}

Start at the feed parsing and link-resolution entry point, using the supplied RSS example with its magnet link to reproduce the malformed URL. Trace how item links are resolved against the feed URL; done means magnet links remain intact and are handed to the magnet: link handler without affecting ordinary relative links.