feat(usage-query): decouple credentials from provider config

Add independent credential fields for usage query to support different
query endpoints and authentication methods.

Changes:
- Add `apiKey` and `baseUrl` fields to UsageScript struct
- Remove dependency on provider config credentials in query_usage
- Update test_usage_script to accept independent credential parameters
- Add credential input fields in UsageScriptModal based on template:
  * General: apiKey + baseUrl
  * NewAPI: baseUrl + accessToken + userId
  * Custom: no additional fields (full freedom)
- Auto-clear irrelevant fields when switching templates
- Add i18n text for "credentialsConfig"

Benefits:
- Query API can use different endpoint/key than provider config
- Better separation of concerns
- More flexible for various usage query scenarios

src-tauri/src/provider.rs

@@ -63,11 +63,19 @@ pub struct UsageScript {
     pub code: String,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub timeout: Option<u64>,
-    /// 访问令牌（用于需要登录的接口）
+    /// 用量查询专用的 API Key（通用模板使用）
+    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(rename = "apiKey")]
+    pub api_key: Option<String>,
+    /// 用量查询专用的 Base URL（通用和 NewAPI 模板使用）
+    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(rename = "baseUrl")]
+    pub base_url: Option<String>,
+    /// 访问令牌（用于需要登录的接口，NewAPI 模板使用）
     #[serde(skip_serializing_if = "Option::is_none")]
     #[serde(rename = "accessToken")]
     pub access_token: Option<String>,
-    /// 用户ID（用于需要用户标识的接口）
+    /// 用户ID（用于需要用户标识的接口，NewAPI 模板使用）
     #[serde(skip_serializing_if = "Option::is_none")]
     #[serde(rename = "userId")]
     pub user_id: Option<String>,