"Dynamic Folders" that automatically contain symbolic links to files matching search criteria

Just getting started with copyparty, loving it so far! I don't know all the features or how it really works behind the scenes but I'm excited to try out the RSS feed functionality. But i thought of a use case that could make them really powerful.

## Problem statement
I want to use copy party to host RSS feeds of my downloaded copies of podcasts. For one podcast, there's 2 "shows" in the original feed- the main show and the "behind the scenes show about the show". These are usually every-other episode and thus it's annoying when you want to just listen to the main show in your podcast app and have to read carefully to get the right episode, skip every other episode, etc.

My thought when I heard about copy party's rss feeds was: oh cool, I could create a folder, put all of Show A into a folder and all of Show B into a second folder, then have multiple rss feeds depending on whether I want to listen to show A or B or A+B or whatever.

The only problem with doing this manually is that the podcast is ongoing and thus new episodes come come out every week. Which would mean manual work to get them into those respective folders every time.

## Thus the feature request is a "Dynamic Folder"

My thought is that you could create a rule set that performs a search on content, and specify an output directory, and then copyparty would run those searches on some kind of basis, and create symlinks to the matching files in the output directory.

So if i had

```
/media/podcasts/Dungeons and Daddies/[No Ads] S1 E1 -> search for "[No Ads]" -> put symlink in /Podcasts/rss/Dungeons And Daddies/Regular Episodes -> check every X hours
/media/podcasts/Dungeons and Daddies/[Talking Dad] S1 E1 -> search for "[Talking Dad]" -> put symlink in /Podcasts/rss/Dungeons And Daddies/Talking Dad -> check every X hours
```

I don't know if copyparty has any kind of background jobs like this so idk if this is a big ask. I've also never heard of a file system doing this kind of thing so this might be way out of left field.

Thanks for all your work on this awesome app! This is obviously very niche and i could just write a little script to do this for me on my NAS if this doesn't match with copyparty's intended use cases.

Look at the media indexer and file scanning logic in copyparty to understand how it currently traverses directories. The feature would need a new background job scheduler and symlink management. Check for existing periodic tasks or cron-like functionality. Determine how to define and store search rules, and how to safely create/remove symlinks in the output directory.

Written by the indexing model from the issue text.