fix(blog): Use focus-visible for topic filter button focus ring (#76)

Change focus ring on topic filter buttons to only appear on keyboard
navigation, not on mouse clicks. This improves UX by removing the
distracting blue circle that appeared when clicking topic badges.

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

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: planeyang

apps/blog/components/essay/EssayFilters.tsx

@@ -158,7 +158,7 @@ export function EssayFilters({
                 key={value}
                 onClick={() => handleTopicToggle(value)}
                 aria-pressed={isSelected}
-                className="essay-filters-topic-btn focus:outline-none focus:ring-2 focus:ring-action-primary focus:ring-offset-2 rounded-full"
+                className="essay-filters-topic-btn focus:outline-none focus-visible:ring-2 focus-visible:ring-action-primary focus-visible:ring-offset-2 rounded-full"
                 data-topic={value}
                 data-selected={isSelected}
               >