refactor(types): rename AppType to AppId for semantic clarity

Rename `AppType` to `AppId` across the entire frontend codebase to better
reflect its purpose as an application identifier rather than a type category.
This aligns frontend naming with backend command parameter conventions.

Changes:
- Rename type `AppType` to `AppId` in src/lib/api/types.ts
- Remove `AppType` export from src/lib/api/index.ts
- Update all component props from `appType` to `appId` (43 files)
- Update all variable names from `appType` to `appId`
- Synchronize documentation (CHANGELOG, refactoring plans)
- Update test files and MSW mocks

BREAKING CHANGE: `AppType` type is no longer exported. Use `AppId` instead.
All component props have been renamed from `appType` to `appId`.

src/components/providers/forms/CodexFormFields.tsx

@@ -80,7 +80,7 @@ export function CodexFormFields({
       {/* 端点测速弹窗 - Codex */}
       {shouldShowSpeedTest && isEndpointModalOpen && (
         <EndpointSpeedTest
-          appType="codex"
+          appId="codex"
           value={codexBaseUrl}
           onChange={onBaseUrlChange}
           initialEndpoints={speedTestEndpoints}