fix: unit page title no longer overlaps the Live/Discussions badges

[AhtishamShahid]

Description

To hide blank space under the sub header's action buttons, the unit page pulled everything below the sub header up by a fixed 35px (.course-unit .sub-header { margin-bottom: -35px }). Once the unit display name wraps to a second line the title, not the buttons, sets the header's height, so those 35px come out of the title and the "Live" / "Discussions Enabled" badges are painted over it.

This zeroes the .sub-header-actions bottom margin inside .course-unit instead, closing the same gap by the right amount at any title height. Scoped to .course-unit, so the shared SubHeader on other pages is untouched.

Before

1000px-wide window, display name wrapping to three lines:

After

Supporting information

Reported as mitodl/hq#12844 (MIT Open Learning, private tracker).

Testing instructions

1. Give a unit a display name long enough to wrap, publish it with the course start date in the past (Live badge), and turn on openedx discussions plus discussion_enabled on the unit (Discussions Enabled badge).
2. Open the unit page at a window width of about 1000px so the title wraps: the badges should sit below the title instead of on top of its last line.
3. Widen until the title fits on one line and confirm the spacing there is unchanged.

Other information

• CSS only. No behaviour, API, dependency, or migration changes.
• Checked by hand on Verawood (openedx-authoring-dev:22.0.0) at 1000px (three-line title), 1500px (two-line title), and with a one-line title. npx stylelint src/course-unit/CourseUnit.scss passes; the Jest suite was not run locally.
• Backported to release/verawood in fix: unit page title no longer overlaps the Live/Discussions badges [backport to verawood] #3244 as the same commit.

Best Practices Checklist

CSS-only change: no new files, components, state, API calls, or translated strings, so none of the checklist items apply.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.02%. Comparing base (87ce85d) to head (0940e69).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3243   +/-   ##
=======================================
  Coverage   96.02%   96.02%           
=======================================
  Files        1401     1401           
  Lines       34129    34129           
  Branches     7842     7842           
=======================================
  Hits        32772    32772           
  Misses       1316     1316           
  Partials       41       41           

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[farhaanbukhsh]

👍

✅ I tested this:

• by creating a big unit name
• the name overlaps on master
• the name is rendered properly on the feature branch.
• played around with the css and the solution looked optimized

✅ I read through the code
✅ I checked for accessibility issues
❌ Includes documentation

[farhaanbukhsh]

Thank you @AhtishamShahid for the fix :)