fix(styles): expand Hypothesis margin override to cover all selectors

The Hypothesis extension injects margin-right: 16px via .headroom-target
and header.headroom selectors. The previous fix only targeted #quarto-header.
Now all three selectors are covered to ensure the header extends full width.

Author: profvjreddi

book/quarto/assets/styles/style.scss

@@ -408,7 +408,9 @@ a {
 }
 
 // Fix Hypothesis margin that prevents full-width elements
-body.hypothesis-enabled #quarto-header {
+body.hypothesis-enabled #quarto-header,
+body.hypothesis-enabled .headroom-target,
+body.hypothesis-enabled header.headroom {
   margin-right: 0 !important;
 }