fix(admin-menu): restore visible background pill on active menu badge

[faisalahammad]

Resolves #8073

Proposed Changes

• Fix the admin menu count badge (.awaiting-mod) on Sensei admin screens: WordPress core's colors.css paints the active menu item's count a near-black background, so the number renders as a bare character with no pill. Add a SCSS override scoped to the li.current item that uses the existing $promo_highlight accent, with :not() exclusions so the Pro-promo pills are unaffected.

Screenshots

Before	After
Active menu badge shows a bare number with no background pill.	Active menu badge shows the number inside the accent-colored pill.

Testing Instructions

• Open wp-admin on a Sensei install with items showing count badges (e.g. Home notices, Grading ungraded)
• Click/navigate so the menu item is the active (current) one
• Confirm the badge number renders inside a visible $promo_highlight pill
• Confirm the sensei pro promo/upsell badges are unchanged (excluded by the :not() selectors)

New/Updated Hooks

N/A

Deprecated Code

N/A

Changelog entry

• Changelog entry committed as changelog/fix-8073-admin-menu-active-badge-color (fork cannot use the automated CI checkbox)

[faisalahammad]

CI check status on this PR.

Psalm (8.2) and PHP Linting both pass at the current head (aece56c). The diff only changes SCSS and changelog, there is no PHP code to check.

Two other checks still fail, both from the fork PR permission model:

1. Check Milestone. The PR has no milestone. Setting it needs a maintainer with write access to the base repo. A fork PR author can not set a milestone through the API. Please set the shipping milestone (4.26.3) to clear this check.

2. Playground PR Preview: Expose Built Artifact. The composer action uploads to the ci-playground-artifacts release and gets HTTP 403 Resource not accessible by integration. This is a fork PR token scope limitation in the WordPress/action-wp-playground-pr-preview action, not a code issue.

No code changes were needed or made for this PR.