Fix pubDate not being added to RSS entries

[ninjack-dev]

Resolves #2103. I went for the simplest possible fix which just uses the parsed date from the file name; since this lacks an actual time, the RSS feed shows new entries as being published at midnight. A more granular fix would be somewhat hacky (e.g. parsing the Git commit metadata on a per-file basis, or requiring that article writers specify date in the frontmatter), so I'd just leave it as-is for now.

Confirmed with:

def getTitlePubDate [] {
  $in | get content.content.0
      | where tag == "item"
      | each {|it|
          {
            title: ($it.content | where tag == "title" | first 1 | get content.0.content.0)
            pubDate: ($it.content | where tag == "pubDate" | first 1 | get content.0.content.0)
          }
        } | first 3 | to md 
}

Running open .vuepress/dist/rss.xml | getTitlePubDate:

title	pubDate
Nushell 0.114.1	Sat, 11 Jul 2026 00:00:00 GMT
Nushell 0.114.0	Sat, 04 Jul 2026 00:00:00 GMT
This week in Nushell #356	Fri, 19 Jun 2026 00:00:00 GMT

[fdncred]

Thanks