Add more prominent registration guidance

[ruf-io]

Description

This is a follow-up on the changes proposed as part of the "reduce spam" initiative.

The goal of these changes is to route people who don't want to genuinely contribute to Open Source into creating PR's on their own repos instead of spammy PR's on big open source repos.

Step 1 of registration UI:

Empty state UI post-registration:

What's still needed: We need a callout when a user has one or more PR's, and maybe a callout when a user has a PR that has been marked as spam or invalid?

Test process

• [ ] Register with a new account, confirm that you see the Do's and Don'ts and they display correctly in light mode and dark mode.
• [ ] Go to profile page, confirm that you see the suggestion panels and they display correctly in light mode and dark mode.
• [ ] Confirm that all links work.
• [ ] Confirm that new required fields must be checked before user can register (quality_acceptance, disqualify_acceptance)
• [ ] Confirm that these fields cannot be checked until video has finished playing.
• [ ] Confirm copy meets new requirements.
• [ ] Confirm mobile view works.

Requirements to merge

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code in hard-to-understand areas
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes

[katjuell]

Updated criteria added to test checklist.