refactor: prevent apiKey field creation for official providers

Improved useApiKeyState hook to explicitly handle category parameter:
- Only create apiKey field for non-official providers in add mode
- Explicitly check category !== undefined to avoid unintended behavior
- Added comprehensive comments explaining the logic
- Updated dependency array to include category parameter

This ensures official provider configs remain clean without empty apiKey fields.

src/components/providers/forms/ProviderForm.tsx

@@ -121,6 +121,7 @@ export function ProviderForm({
     initialConfig: form.watch("settingsConfig"),
     onConfigChange: (config) => form.setValue("settingsConfig", config),
     selectedPresetId,
+    category,
   });
 
   // 使用 Base URL hook (仅 Claude 模式)

src/components/providers/forms/hooks/useApiKeyState.ts

@@ -1,4 +1,5 @@
 import { useState, useCallback } from "react";
+import type { ProviderCategory } from "@/types";
 import {
   getApiKeyFromConfig,
   setApiKeyInConfig,
@@ -9,6 +10,7 @@ interface UseApiKeyStateProps {
   initialConfig?: string;
   onConfigChange: (config: string) => void;
   selectedPresetId: string | null;
+  category?: ProviderCategory;
 }
 
 /**
@@ -19,6 +21,7 @@ export function useApiKeyState({
   initialConfig,
   onConfigChange,
   selectedPresetId,
+  category,
 }: UseApiKeyStateProps) {
   const [apiKey, setApiKey] = useState(() => {
     if (initialConfig) {
@@ -35,14 +38,21 @@ export function useApiKeyState({
         initialConfig || "{}",
         key.trim(),
         {
+          // 最佳实践：仅在"新增模式"且"非官方类别"时补齐缺失字段
+          // - 新增模式：selectedPresetId !== null
+          // - 非官方类别：category !== undefined && category !== "official"
+          // - 官方类别：不创建字段（UI 也会禁用输入框）
+          // - 未传入 category：不创建字段（避免意外行为）
           createIfMissing:
-            selectedPresetId !== null && selectedPresetId !== "custom",
+            selectedPresetId !== null &&
+            category !== undefined &&
+            category !== "official",
         },
       );
 
       onConfigChange(configString);
     },
-    [initialConfig, selectedPresetId, onConfigChange],
+    [initialConfig, selectedPresetId, category, onConfigChange],
   );
 
   const showApiKey = useCallback(