Tint strength and blur strength values not stored correctly

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• This is not a feature request
• This is not an image-provider request
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Describe the bug:
When trying to change tint strength or blur strength in the Admin/Theming settings, the backrgound appearance doesn't change and, after a page reload, the sliders are back to their default values.

To Reproduce:

1. Turn on tinting.
2. Try to change tint strength and/or blur strength in Admin/Theming settings.

Expected behavior:
Background gets updated accordingly and sliders store correct values.

Server:

• Nextcloud version: 31.0.10
• Splash-App version: 3.1.0

Additional Information:
These two lines always set the returned value to the default value (30 and 0).
https://github.com/nextcloud/unsplash/blob/ff2ac675c256104c6b16c672bd6a1f688e9d020b/templates/settings/admin.php#L131
https://github.com/nextcloud/unsplash/blob/ff2ac675c256104c6b16c672bd6a1f688e9d020b/templates/settings/admin.php#L138

Start in templates/settings/admin.php at the two lines linked in the issue, then reproduce the tint and blur changes from Admin/Theming settings and reload the page. Trace how those values are returned and used; done means the background updates and both sliders retain their selected values after reload.