feat(yomitan): add read-only external profile support for shared dictionaries (#18)

src/main/runtime/character-dictionary-availability.ts

@@ -0,0 +1,10 @@
+export function isCharacterDictionaryRuntimeEnabled(externalProfilePath: string): boolean {
+  return externalProfilePath.trim().length === 0;
+}
+
+export function getCharacterDictionaryDisabledReason(externalProfilePath: string): string | null {
+  if (isCharacterDictionaryRuntimeEnabled(externalProfilePath)) {
+    return null;
+  }
+  return 'Character dictionary is disabled while yomitan.externalProfilePath is configured.';
+}