fix: use fixed height for profile header (6:1 ratio at max-width)

Change header display from aspect-ratio: 3/1 to a fixed height of 128px
(theme.space['32']). This achieves a 6:1 aspect ratio at the 768px
max-width container, and the ratio naturally decreases on mobile as the
width shrinks while height remains constant.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: storywithoutend

src/components/ProfileSnippet.tsx

@@ -43,13 +43,12 @@ const HeaderContainer = styled.div<{ $header?: string }>(
     ${$header
       ? `
     background-image: url("${encodeURI($header)}")};
-    aspect-ratio: 3 / 1;
+    height: ${theme.space['32']};
     `
       : `
         background-image: ${theme.colors.blueGradient};
         height: ${theme.space['28']};
     `}
-    /* aspect-ratio: 3 / 1; */
     background-position: center;
     background-size: cover;
     background-repeat: no-repeat;