Self-review: drop inert font-size/weight resets from the heading rule

The UI33 heading reset only needs to zero the UA margin — every heading in the
app carries a Fluent typography class that out-specifies this element selector
(and there are no raw headings), so the font-size/font-weight `inherit` lines
never applied and contradicted the comment. Keep just `margin: 0`.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/renderer/src/assets/base.css

@@ -10,11 +10,11 @@
 }
 
 /*
- * Reset the UA heading styles (UI33). Titles are rendered as real headings
+ * Zero the UA heading margin (UI33). Titles are rendered as real headings
  * (h1/h2) for Narrator heading-navigation, but they carry Fluent's typography
- * classes for their visual ramp; those classes out-specify this element
- * selector, so only the browser's default heading margin needs zeroing to keep
- * the layout identical to the former styled-span titles.
+ * classes for their visual ramp (font size/weight/line-height); those classes
+ * out-specify this element selector, so only the browser's default heading
+ * margin needs removing to keep the layout identical to the former span titles.
  */
 h1,
 h2,
@@ -23,8 +23,6 @@ h4,
 h5,
 h6 {
   margin: 0;
-  font-size: inherit;
-  font-weight: inherit;
 }
 
 html,