fix: improve collapsed highlights panel button placement

- Change chevron to point right (rotation 180) when collapsed
- Position button at top-left instead of center
- Align with header position for consistency
- Adjust padding to match expanded state header

The expand button now appears at the top of the panel
next to where the highlight count would be, making it
more intuitive and consistent with the UI.

src/components/HighlightsPanel.tsx

@@ -66,7 +66,7 @@ export const HighlightsPanel: React.FC<HighlightsPanelProps> = ({
           title="Expand highlights panel"
           aria-label="Expand highlights panel"
         >
-          <FontAwesomeIcon icon={faChevronLeft} />
+          <FontAwesomeIcon icon={faChevronLeft} rotation={180} />
         </button>
       </div>
     )