feat(vocab): restore manual hard vocabulary removal

frontend/src/views/social/VocabCourseView.vue

@@ -46,6 +46,13 @@
               <strong>{{ entry.learning }}</strong>
               <span>{{ entry.reference }}</span>
             </div>
+            <button
+              type="button"
+              class="button-secondary course-hard-list__remove"
+              @click="unmarkHardVocab(entry)"
+            >
+              {{ $t('socialnetwork.vocab.courses.unmarkVocabHard') }}
+            </button>
           </div>
         </div>
       </section>
@@ -606,6 +613,21 @@ export default {
         this.hardVocabList = [];
       }
     },
+    async unmarkHardVocab(entry) {
+      const itemKey = String(entry?.itemKey || entry?.key || '').trim();
+      if (!itemKey || !this.courseId) return;
+      try {
+        await apiClient.patch('/api/vocab/srs/hard', {
+          courseId: this.courseId,
+          itemKey
+        });
+        this.hardVocabList = this.hardVocabList
+          .filter((item) => String(item?.itemKey || item?.key || '').trim() !== itemKey);
+      } catch (error) {
+        console.warn('Konnte die Hart-Markierung nicht entfernen:', error);
+        await this.refreshHardVocabList();
+      }
+    },
     handleWindowFocus() {
       this.refreshHardVocabList();
       this.syncSrsSessionProgress();