chore: update CI configuration and enhance test stability

- Added deterministic API key and environment variables in e2e-tests.yml to ensure consistent test behavior.
- Refactored CodexProvider tests to improve type safety and mock handling, ensuring reliable test execution.
- Updated provider-factory tests to mock installation detection for CodexProvider, enhancing test isolation.
- Adjusted Playwright configuration to conditionally use external backend, improving flexibility in test environments.
- Enhanced kill-test-servers script to handle external server scenarios, ensuring proper cleanup of test processes.

These changes improve the reliability and maintainability of the testing framework, leading to a more stable development experience.

apps/server/tests/unit/providers/provider-factory.test.ts

@@ -2,18 +2,36 @@ import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
 import { ProviderFactory } from '@/providers/provider-factory.js';
 import { ClaudeProvider } from '@/providers/claude-provider.js';
 import { CursorProvider } from '@/providers/cursor-provider.js';
+import { CodexProvider } from '@/providers/codex-provider.js';
 
 describe('provider-factory.ts', () => {
   let consoleSpy: any;
+  let detectClaudeSpy: any;
+  let detectCursorSpy: any;
+  let detectCodexSpy: any;
 
   beforeEach(() => {
     consoleSpy = {
       warn: vi.spyOn(console, 'warn').mockImplementation(() => {}),
     };
+
+    // Avoid hitting real CLI / filesystem checks during unit tests
+    detectClaudeSpy = vi
+      .spyOn(ClaudeProvider.prototype, 'detectInstallation')
+      .mockResolvedValue({ installed: true });
+    detectCursorSpy = vi
+      .spyOn(CursorProvider.prototype, 'detectInstallation')
+      .mockResolvedValue({ installed: true });
+    detectCodexSpy = vi
+      .spyOn(CodexProvider.prototype, 'detectInstallation')
+      .mockResolvedValue({ installed: true });
   });
 
   afterEach(() => {
     consoleSpy.warn.mockRestore();
+    detectClaudeSpy.mockRestore();
+    detectCursorSpy.mockRestore();
+    detectCodexSpy.mockRestore();
   });
 
   describe('getProviderForModel', () => {