fix: Allow testing API keys without saving first

- Add optional apiKey parameter to verifyClaudeAuth endpoint
- Backend uses provided key when available, falls back to stored key
- Frontend passes current input value to test unsaved keys
- Add input validation before testing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/ui/src/lib/http-api-client.ts

@@ -491,12 +491,13 @@ export class HttpApiClient implements ElectronAPI {
     }> => this.get('/api/setup/platform'),
 
     verifyClaudeAuth: (
-      authMethod?: 'cli' | 'api_key'
+      authMethod?: 'cli' | 'api_key',
+      apiKey?: string
     ): Promise<{
       success: boolean;
       authenticated: boolean;
       error?: string;
-    }> => this.post('/api/setup/verify-claude-auth', { authMethod }),
+    }> => this.post('/api/setup/verify-claude-auth', { authMethod, apiKey }),
 
     getGhStatus: (): Promise<{
       success: boolean;