Add Vocab Trainer feature with routing, database schema, and translations

- Introduced Vocab Trainer functionality, including new routes for managing languages and chapters.
- Implemented database schema for vocab-related tables to ensure data integrity.
- Updated navigation and UI components to include Vocab Trainer in the social network menu.
- Added translations for Vocab Trainer in both German and English locales, enhancing user accessibility.

frontend/src/views/social/VocabSubscribeView.vue

@@ -0,0 +1,93 @@
+<template>
+  <h2>{{ $t('socialnetwork.vocab.subscribeTitle') }}</h2>
+
+  <div class="box">
+    <p>{{ $t('socialnetwork.vocab.subscribeHint') }}</p>
+
+    <label class="label">
+      {{ $t('socialnetwork.vocab.shareCode') }}
+      <input v-model="shareCode" type="text" />
+    </label>
+
+    <div class="actions">
+      <button :disabled="saving || !canSave" @click="subscribe">
+        {{ saving ? $t('socialnetwork.vocab.saving') : $t('socialnetwork.vocab.subscribe') }}
+      </button>
+      <button :disabled="saving" @click="back">{{ $t('general.back') }}</button>
+    </div>
+  </div>
+</template>
+
+<script>
+import { mapActions } from 'vuex';
+import apiClient from '@/utils/axios.js';
+
+export default {
+  name: 'VocabSubscribeView',
+  data() {
+    return {
+      shareCode: '',
+      saving: false,
+    };
+  },
+  computed: {
+    canSave() {
+      return this.shareCode.trim().length >= 6;
+    },
+  },
+  methods: {
+    ...mapActions(['loadMenu']),
+    back() {
+      this.$router.push('/socialnetwork/vocab');
+    },
+    async subscribe() {
+      this.saving = true;
+      try {
+        const res = await apiClient.post('/api/vocab/subscribe', { shareCode: this.shareCode });
+        try { await this.loadMenu(); } catch (_) {}
+        const langId = res.data?.languageId;
+        this.$root.$refs.messageDialog?.open(
+          this.$t('socialnetwork.vocab.subscribeSuccess'),
+          this.$t('socialnetwork.vocab.subscribeTitle')
+        );
+        if (langId) {
+          this.$router.push(`/socialnetwork/vocab/${langId}`);
+        }
+      } catch (e) {
+        console.error('Subscribe failed:', e);
+        this.$root.$refs.messageDialog?.open(
+          this.$t('socialnetwork.vocab.subscribeError'),
+          this.$t('error.title')
+        );
+      } finally {
+        this.saving = false;
+      }
+    },
+  },
+  mounted() {
+    // optional: ?code=... unterstützt
+    const code = this.$route?.query?.code;
+    if (typeof code === 'string' && code.trim()) {
+      this.shareCode = code.trim();
+    }
+  },
+};
+</script>
+
+<style scoped>
+.box {
+  background: #f6f6f6;
+  padding: 12px;
+  border: 1px solid #ccc;
+}
+.label {
+  display: block;
+  margin-bottom: 10px;
+}
+.actions {
+  display: flex;
+  gap: 8px;
+}
+</style>
+
+