fix(dictionary): block --yomitan when an external profile is configured

- Keep read-only external-profile mode while Hachidori is active by checking the configured externalProfilePath
- Hachidori settings remain available
- Smoke check asserts the external-profile block, with a --bundled-yomitan path for the bundled case
- Update usage docs and changelog fragment

src/main.ts

@@ -5226,7 +5226,7 @@ function initializeOverlayRuntime(): void {
 
 function openYomitanSettings(): boolean {
   if (activeDictionaryBackend === 'hachidori') {
-    if (yomitanProfilePolicy.isExternalReadOnlyMode()) {
+    if (configService.getConfig().yomitan.externalProfilePath.trim()) {
       logger.warn('Yomitan settings unavailable while using read-only external-profile mode.');
       return false;
     }