Add quick-win tests for components and hooks

Adds tests for DifficultyIndicator, Toast, RollModeMenu, OverflowMenu,
useTheme, and useRulesEdition. Covers rendering, user interactions,
auto-dismiss timers, external store sync, and localStorage persistence.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vitest.config.ts

@@ -26,16 +26,16 @@ export default defineConfig({
 					branches: 70,
 				},
 				"apps/web/src/hooks": {
-					lines: 59,
-					branches: 41,
+					lines: 64,
+					branches: 48,
 				},
 				"apps/web/src/components": {
-					lines: 49,
-					branches: 47,
+					lines: 52,
+					branches: 49,
 				},
 				"apps/web/src/components/ui": {
-					lines: 73,
-					branches: 67,
+					lines: 83,
+					branches: 74,
 				},
 			},
 		},