refactor: update authentication handling and model configuration

- Enhanced authentication method validation in `auth.ts` and `auth.test.ts`.
- Introduced new model provider configuration logic
- Updated environment variable handling for various auth types.
- Removed deprecated utility functions and tests related to fallback mechanisms.

packages/cli/src/ui/hooks/useToolScheduler.test.ts

@@ -62,7 +62,7 @@ const mockConfig = {
   getAllowedTools: vi.fn(() => []),
   getContentGeneratorConfig: () => ({
     model: 'test-model',
-    authType: 'gemini-api-key',
+    authType: 'gemini',
   }),
   getUseSmartEdit: () => false,
   getUseModelRouter: () => false,