feat(VocabPracticeDialog): add answer variant expansion for improved vocabulary training

- Introduced a new method `expandAnswerVariants` to generate multiple answer variants from a given input, enhancing the flexibility of acceptable answers.
- Improved handling of words with slashes to create diverse answer options, ensuring a richer vocabulary training experience.
- Updated the answer collection logic to utilize the new method, allowing for a broader range of valid responses during practice sessions.

frontend/src/dialogues/socialnetwork/VocabPracticeDialog.vue

@@ -543,11 +543,52 @@ export default {
         const itemPrompt = direction === 'L2R' ? item.learning : item.reference;
         if (this.normalize(itemPrompt) === p) {
           const a = direction === 'L2R' ? item.reference : item.learning;
-          answers.add(a);
+          this.expandAnswerVariants(a).forEach((variant) => answers.add(variant));
         }
       }
       return Array.from(answers);
     },
+    expandAnswerVariants(answer) {
+      const base = String(answer || '').trim();
+      if (!base) return [];
+
+      const words = base.split(/\s+/).map((word) => {
+        if (!word.includes('/')) {
+          return [word];
+        }
+
+        const match = word.match(/^([([{„"'“‘]*)(.*?)([)\]}.,!?;:»"'”’]*)$/);
+        const prefix = match?.[1] || '';
+        const core = match?.[2] || word;
+        const suffix = match?.[3] || '';
+        const parts = core
+          .split('/')
+          .map((part) => part.trim())
+          .filter(Boolean);
+
+        if (parts.length < 2 || parts.length > 4) {
+          return [word];
+        }
+
+        return parts.map((part) => `${prefix}${part}${suffix}`);
+      });
+
+      const variants = [''];
+      for (const options of words) {
+        const next = [];
+        for (const current of variants) {
+          for (const option of options) {
+            next.push(`${current}${current ? ' ' : ''}${option}`);
+          }
+        }
+        if (next.length > 24) {
+          return [base];
+        }
+        variants.splice(0, variants.length, ...next);
+      }
+
+      return [...new Set([base, ...variants])];
+    },
     computeWeight(item) {
       const st = this.perId[item.id] || { c: 0, w: 0, streak: 0, lastAsked: 0 };
       let w = 1;