refactor(components): convert const to reactive where appropriate

- Inline class assignments to avoid script-level clutter
- Ignore a11y-missing-attribute instead of redundant href

src/components/FileUploader/FileUploaderButton.svelte

@@ -15,15 +15,15 @@
 
   import { cx } from '../../lib';
 
-  const _class = cx(
+  let inputRef = undefined;
+
+  $: _class = cx(
     '--btn',
     '--btn--sm',
     kind && `--btn--${kind}`,
     disabled && '--btn--disabled',
     className
   );
-
-  let inputRef = undefined;
 </script>
 
 <label