refactor: replace export* barrels with explicit named exports

Wildcard re-exports obscure each slice public surface and weaken
tree-shaking. Convert to explicit named re-exports with export/export
type split (B-1) for ComparisonView, ChangeAppTheme, Breadcrumb/model,
and FilterAndSortFonts/api barrels.

src/widgets/ComparisonView/index.ts

@@ -1,2 +1,3 @@
-export * from './model';
+export { getComparisonStore } from './model';
+export type { Side } from './model';
 export { ComparisonView } from './ui';