fix(provider-form): reset baseUrl and apiKey states when switching presets

Fix state synchronization in useBaseUrlState and useApiKeyState hooks
to properly clear values when config is reset. Previously, when switching
from a preset to "custom", the baseUrl and apiKey states would retain
their old values because the sync logic only updated when new values
existed, not when they were cleared.

Changes:
- useBaseUrlState: Always sync baseUrl to config value (empty if undefined)
- useApiKeyState: Remove hasApiKeyField check that prevented clearing

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

@@ -43,11 +43,7 @@ export function useApiKeyState({
       return;
     }
 
-    // 仅当配置确实包含 API Key 字段时才同步（避免无意清空用户正在输入的 key）
-    if (!hasApiKeyField(initialConfig, appType)) {
-      return;
-    }
-
+    // 从配置中提取 API Key（如果不存在则返回空字符串）
     const extracted = getApiKeyFromConfig(initialConfig, appType);
     if (extracted !== apiKey) {
       setApiKey(extracted);

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

@@ -41,8 +41,9 @@ export function useBaseUrlState({
     try {
       const config = JSON.parse(settingsConfig || "{}");
       const envUrl: unknown = config?.env?.ANTHROPIC_BASE_URL;
-      if (typeof envUrl === "string" && envUrl && envUrl.trim() !== baseUrl) {
-        setBaseUrl(envUrl.trim());
+      const nextUrl = typeof envUrl === "string" ? envUrl.trim() : "";
+      if (nextUrl !== baseUrl) {
+        setBaseUrl(nextUrl);
       }
     } catch {
       // ignore