feat(vocab): add language and course dictionary endpoints and UI components

- Implemented `getLanguageDictionary` and `getCourseDictionary` methods in the VocabService to retrieve vocabulary entries filtered by search terms.
- Updated VocabController and vocabRouter to include new routes for accessing language and course dictionaries.
- Enhanced frontend components to navigate to the new dictionary views, including buttons in VocabCourseView and VocabLanguageView.
- Added localization entries for the dictionary feature in multiple languages, ensuring a consistent user experience across the platform.

frontend/src/i18n/locales/de/general.json

@@ -148,6 +148,7 @@
             "subscribeLanguage": "Sprache abonnieren",
             "language": "Sprache",
             "chapter": "Kapitel",
+            "vocabDictionary": "Wörterbuch",
             "courses": "Kurse",
             "course": "Kurs",
             "lesson": "Lektion",