fix: apply CSS module class for active Shop category filter

Claude-Session: https://claude.ai/code/session_01NhxA4npAXAxmCDEJt6kxSH

src/pages/Shop.tsx

@@ -18,7 +18,7 @@ function Shop() {
           <button
             key={c}
             type="button"
-            className={c === category ? 'active' : ''}
+            className={c === category ? styles.active : ''}
             onClick={() => setCategory(c)}
           >
             {c.replace('-', ' ')}