refactor: centralize action/icon button styles across all tools

Extract shared actionBtn and iconBtn constants into lib/utils/styles.ts
and replace all 11 local definitions across tool components.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/utils/index.ts

@@ -4,3 +4,4 @@ export * from './urlSharing';
 export * from './animations';
 export * from './format';
 export * from './time';
+export * from './styles';