Refactor vocabulary search functionality in VocabService and update UI components

- Modified the searchVocabs method in VocabService to consolidate search parameters into a single query term for improved flexibility.
- Updated VocabSearchDialog to replace separate input fields for mother tongue and learning language with a unified search term input.
- Adjusted button logic to enable search only when a term is provided, enhancing user experience.
- Added new translations for the search term in both German and English locales to support the updated UI.

frontend/src/dialogues/socialnetwork/VocabSearchDialog.vue

@@ -16,14 +16,10 @@
       <div class="top">
         <div class="row">
           <label class="field">
-            {{ $t('socialnetwork.vocab.search.motherTongue') }}
-            <input v-model="motherTongue" type="text" @keydown.enter.prevent="runSearch" />
+            {{ $t('socialnetwork.vocab.search.term') }}
+            <input v-model="term" type="text" @keydown.enter.prevent="runSearch" />
           </label>
-          <label class="field">
-            {{ learningLabel }}
-            <input v-model="learning" type="text" @keydown.enter.prevent="runSearch" />
-          </label>
-          <button class="btn" :disabled="loading || (!motherTongue.trim() && !learning.trim())" @click="runSearch">
+          <button class="btn" :disabled="loading || !term.trim()" @click="runSearch">
             {{ loading ? $t('general.loading') : $t('socialnetwork.vocab.search.search') }}
           </button>
         </div>
@@ -66,8 +62,7 @@ export default {
     return {
       languageId: null,
       languageName: '',
-      motherTongue: '',
-      learning: '',
+      term: '',
       loading: false,
       results: [],
       error: '',
@@ -85,8 +80,7 @@ export default {
     open({ languageId, languageName = '' } = {}) {
       this.languageId = languageId;
       this.languageName = languageName || '';
-      this.motherTongue = '';
-      this.learning = '';
+      this.term = '';
       this.results = [];
       this.error = '';
       this.loading = false;
@@ -98,17 +92,15 @@ export default {
     },
     async runSearch() {
       if (!this.languageId) return;
-      const mt = this.motherTongue.trim();
-      const l = this.learning.trim();
-      if (!mt && !l) return;
+      const q = this.term.trim();
+      if (!q) return;
 
       this.loading = true;
       this.error = '';
       try {
         const res = await apiClient.get(`/api/vocab/languages/${this.languageId}/search`, {
           params: {
-            motherTongue: mt || undefined,
-            learning: l || undefined,
+            q,
           },
         });
         this.results = res.data?.results || [];

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

@@ -312,6 +312,7 @@
             "search": {
                 "open": "Suche",
                 "title": "Vokabeln suchen",
+                "term": "Suchbegriff",
                 "motherTongue": "Muttersprache",
                 "learningLanguage": "Lernsprache",
                 "lesson": "Lektion",

frontend/src/i18n/locales/en/socialnetwork.json

@@ -312,6 +312,7 @@
             "search": {
                 "open": "Search",
                 "title": "Search vocabulary",
+                "term": "Search term",
                 "motherTongue": "Mother tongue",
                 "learningLanguage": "Learning language",
                 "lesson": "Lesson",