五个动物分类合并为单一动物分类，采用子分类分组展示

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

LearnEnglish/LearnEnglish/Resources/words.json

@@ -49,9 +49,13 @@
       ]
     },
     {
-      "id": "land_animals",
+      "id": "animals",
-      "name": "陆地动物",
+      "name": "动物",
       "icon": "pawprint.fill",
+      "words": [],
+      "subcategories": [
+        {
+          "name": "陆地动物",
           "words": [
             { "word": "cat", "phonetic": "/kæt/", "meaning": "猫", "example": "The cat is cute.", "exampleMeaning": "这只猫很可爱。" },
             { "word": "dog", "phonetic": "/dɔːɡ/", "meaning": "狗", "example": "The dog is running.", "exampleMeaning": "狗在跑。" },
@@ -85,9 +89,7 @@
           ]
         },
         {
-      "id": "flying_animals",
           "name": "飞翔动物",
-      "icon": "bird.fill",
           "words": [
             { "word": "bird", "phonetic": "/bɜːrd/", "meaning": "鸟", "example": "The bird can fly.", "exampleMeaning": "鸟会飞。" },
             { "word": "owl", "phonetic": "/aʊl/", "meaning": "猫头鹰", "example": "The owl sleeps in the day.", "exampleMeaning": "猫头鹰白天睡觉。" },
@@ -108,9 +110,7 @@
           ]
         },
         {
-      "id": "waterfowl_animals",
           "name": "水禽",
-      "icon": "bird",
           "words": [
             { "word": "duck", "phonetic": "/dʌk/", "meaning": "鸭子", "example": "The duck swims in the pond.", "exampleMeaning": "鸭子在池塘里游泳。" },
             { "word": "swan", "phonetic": "/swɑːn/", "meaning": "天鹅", "example": "The swan is white.", "exampleMeaning": "天鹅是白色的。" },
@@ -119,9 +119,7 @@
           ]
         },
         {
-      "id": "amphibious_animals",
           "name": "两栖动物",
-      "icon": "leaf.arrow.triangle.circlepath",
           "words": [
             { "word": "frog", "phonetic": "/frɔːɡ/", "meaning": "青蛙", "example": "The frog can jump high.", "exampleMeaning": "青蛙能跳得很高。" },
             { "word": "tadpole", "phonetic": "/ˈtædpoʊl/", "meaning": "蝌蚪", "example": "The tadpole will become a frog.", "exampleMeaning": "蝌蚪会变成青蛙。" },
@@ -129,9 +127,7 @@
           ]
         },
         {
-      "id": "aquatic_animals",
           "name": "水中动物",
-      "icon": "fish.fill",
           "words": [
             { "word": "fish", "phonetic": "/fɪʃ/", "meaning": "鱼", "example": "The fish swims fast.", "exampleMeaning": "鱼游得很快。" },
             { "word": "crayfish", "phonetic": "/ˈkreɪfɪʃ/", "meaning": "小龙虾", "example": "The crayfish lives in the river.", "exampleMeaning": "小龙虾生活在河里。" },
@@ -153,6 +149,8 @@
             { "word": "whale", "phonetic": "/weɪl/", "meaning": "鲸鱼", "example": "The whale is very big.", "exampleMeaning": "鲸鱼非常大。" },
             { "word": "shark", "phonetic": "/ʃɑːrk/", "meaning": "鲨鱼", "example": "The shark has sharp teeth.", "exampleMeaning": "鲨鱼有锋利的牙齿。" }
           ]
+        }
+      ]
     },
     {
       "id": "fruits",