Change Podcast title text colour and/or make "Pattern Image" a mandatory field for Suggest a Podcast form

[ellativity]

Describe the bug
The Podcast page always displays title text in white on a white background, regardless of the user's theme. .

Right now, the Suggest a Podcast form can be submitted without uploading a Pattern Image, which means that when the podcast is approved, the title text is white type on a light background (irrespective of selected theme).

To Reproduce

1. Go to Suggest a Podcast
2. Submit a podcast without uploading a Pattern Image
3. Go to Podcast Admin
4. Approve the podcast by scrolling to the bottom of the page and checking the Published box and clicking Update Podcast button
5. View podcast page by scrolling to the top of the page and clicking the View button
6. Toggle between themes to see if it's just you
7. Cry

Expected behavior

Either the podcast title text displays dark-on-light and light-on-dark, or the Suggest a Podcast form doesn't allow for a podcast to be submitted without uploading a Pattern Image (and specifies why).

Additional context

This is pretty much an admin issue, since we end up fixing the cases where a podcast is submitted without a background and the text is invisible. However, we have no way of knowing that a background wasn't uploaded until we publish the podcast and view the page for ourselves, so it's an extra bunch of steps:

1. find a suitable background for the podcast
2. go back to the podcast edit page
3. upload the background
4. view again to make sure it worked this time.

There is also an issue of uploaded pattern images tiling in unattractive ways, but it's the least of our concerns right now... (see all the screenshots)

[github-actions]

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