fix: translate error message to chinese and clear error state on user input

Author: 许君山

backend/server.js

@@ -95,7 +95,7 @@ app.get('/api/conjugate', (req, res) => {
       type = detectVerbType(processedVerb);
       if (!type) {
         return res.status(400).json({ 
-          error: `Could not automatically detect verb type for '${verb}' (parsed as '${processedVerb}'). Please ensure it is a valid dictionary form Japanese verb or provide the type manually.` 
+          error: `无法自动识别 "${verb}" (解析为 "${processedVerb}") 的动词类型。请确保输入的是正确的日语动词原形（如：食べる、飲む、勉強する）。` 
         });
       }
     }

frontend/src/App.vue

@@ -19,6 +19,7 @@
               type="text"
               placeholder="例如：飲む、食べる、nomu、taberu"
               @keyup.enter="conjugate"
+              @input="error = ''"
               @focus="showSuggestions = true"
               @blur="hideSuggestionsWithDelay"
               autocomplete="off"