chore: remove legacy Pure CSS classes

- Remove all unused pure-button styles
- Clean up legacy CSS compatibility code
- Reduce CSS file size by removing unnecessary styles

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

Co-Authored-By: Claude <[email protected]>

Author: vinta

browser_extensions/chrome/stylesheets/styles.css

@@ -554,62 +554,3 @@ a:hover {
 .mb-2 { margin-bottom: var(--spacing-2); }
 .mb-4 { margin-bottom: var(--spacing-4); }
 
-/* Legacy Pure CSS compatibility (will be removed later) */
-.pure-button {
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  padding: var(--spacing-2) var(--spacing-4);
-  font-size: var(--text-sm);
-  font-weight: 500;
-  border-radius: var(--radius);
-  cursor: pointer;
-  user-select: none;
-  transition: all var(--transition-fast);
-  text-decoration: none;
-  background-color: var(--color-surface-secondary);
-  color: var(--color-text-primary);
-  border: 1px solid var(--color-border);
-}
-
-.pure-button:hover {
-  background-color: var(--color-surface-tertiary);
-}
-
-.pure-button-primary {
-  background-color: var(--color-primary);
-  color: var(--color-text-on-primary);
-  border-color: var(--color-primary);
-}
-
-.pure-button-primary:hover {
-  background-color: var(--color-primary-hover);
-}
-
-.pure-button-blue {
-  background-color: var(--color-primary);
-  color: var(--color-text-on-primary);
-  border-color: var(--color-primary);
-}
-
-.pure-button-green {
-  background-color: var(--color-success);
-  color: var(--color-text-on-primary);
-  border-color: var(--color-success);
-}
-
-.pure-button-purple {
-  background-color: var(--color-secondary);
-  color: var(--color-text-on-primary);
-  border-color: var(--color-secondary);
-}
-
-.big-button {
-  padding: var(--spacing-3) var(--spacing-6);
-  font-size: var(--text-base);
-}
-
-.small-button {
-  padding: var(--spacing-1) var(--spacing-3);
-  font-size: var(--text-xs);
-}