AO3-7388 Redirect to user skin page with error if trying to preview a skin you can't use

[brianjaustin]

This reverts commit 8c294d1. It reintroduces #5776.

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• 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)
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Issue

https://otwarchive.atlassian.net/browse/AO3-7388

Purpose

Redirects to the user skins page when trying to preview a skin that can't be used but can be viewed while logged in as a user. This includes parent-only site skins and work skins. For skins that a logged-in user cannot view (not owned and not public), they are redirected to their dashboard with an error.

Changed preview to a user-only action. Redirects to the login page with an error when trying to preview any skin while logged out. Redirects to the root page with an error when trying to preview any skin while logged in as an admin.

Testing Instructions

For site skins, refer to Jira.

For work skins:

1. Log in
2. Make a work skin
   a. Hi, username! > My Dashboard > Skins > Create Work Skin
   b. Fill in required information
   c. Press “Submit” to save
3. In your browser address bar, add /preview to the end of the skin URL and press Return

For not owned, not public skins:

1. Log in
2. Make a site skin
   a. Hi, username! > My Dashboard > Skins > Create Site Skin
   b. Fill in required information
   c. Press “Submit” to save
3. Copy the site skin URL
4. Log into another account and paste the site skin URL into the browser address bar. Add /preview to the end of the URL and press Return

Credit

zrei (she/they)