AO3-7432 Fix 500 error when leaving kudos with JavaScript disabled

[evanwhitt]

Pull Request Checklist

• Have you read "How to write the perfect pull request"?
• Have you read the contributing guidelines?
• Have you added tests for any changed functionality?
• Have you added the Jira issue number as the first thing in your pull request title (e.g. AO3-1234 Fix thing)
• Do you have fewer than 5 pull requests already open? If not, please wait until they are reviewed and merged before creating new pull requests.

Issue

https://otwarchive.atlassian.net/browse/AO3-7432

Purpose

Leaving kudos with JavaScript disabled can 500 if the page you're on already has an anchor in the URL (e.g. you're at the bookmark form, so the URL ends in #bookmark-form).

The kudos redirect just glued #kudos_message onto the referer URL, which gives you something like ...#bookmark-form#kudos_message. Ruby's URI parser rejects the # inside the fragment, so Rails' open redirect protection throws OpenRedirectError and you get a 500.

Fix: strip any existing anchor from the redirect target before adding #kudos_message.

Testing Instructions

Smoke test as per the Jira issue:

1. Disable JavaScript in your browser.
2. Go to a work.
3. Press the Kudos button.
4. You should be redirected to the work with #kudos_message at the end of the URL, taking you to the success or error message.
5. Repeat while scrolled to the bookmark form (URL ends in #bookmark-form) to confirm no 500.

Credit

Evan W (he/him) [b1ume]