Remove "new" badge from Appearance settings tab

[donnapep]

Proposed Changes

Removes the "new" badge that appeared beside the Appearance tab of Sensei's settings. Learning Mode isn't that new anymore.

Testing Instructions

1. Go to Sensei's setting.
2. Ensure there is no "new" badge beside the Appearance tab.

Pre-Merge Checklist

• PR title and description contain sufficient detail and accurately describe the changes
• Adheres to coding standards (PHP, JavaScript, CSS, HTML)
• All strings are translatable (without concatenation, handles plurals)
• Follows our naming conventions (P6rkRX-4oA-p2)
• Hooks (p6rkRX-1uS-p2) and functions are documented
• New UIs are responsive and use a mobile-first approach
• Code is tested on the minimum supported PHP and WordPress versions

[Copilot]

Pull request overview

This PR removes the "new" badge from the Appearance settings tab in Sensei LMS, as the Learning Mode feature is no longer considered new.

• Removes badge property from appearance-settings section definition
• Removes badge rendering logic from settings tabs display
• Removes associated CSS styling for settings tab badges

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
includes/class-sensei-settings.php	Removes the 'badge' property from the appearance-settings section array
includes/class-sensei-settings-api.php	Removes badge handling logic from settings_tabs() method including badge property assignment and HTML rendering
changelog/remove-new-label-appearance-settings	Adds changelog entry documenting the removal of the badge as a minor, removed-type change
assets/css/settings.scss	Removes the .sensei-settings-tab__badge CSS class and its styling rules

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[donnapep]

Merging as test failures are unrelated to these changes.