feat: implement simple query service and enhance provider abstraction

- Introduced a new Simple Query Service to streamline basic AI queries, allowing for structured JSON outputs.
- Updated existing routes to utilize the new service, replacing direct SDK calls with a unified interface for querying.
- Enhanced provider handling in various routes, including generate-spec, generate-features-from-spec, and validate-issue, to support both Claude and Cursor models seamlessly.
- Added structured output support for improved response handling and error management across the application.

apps/server/src/providers/index.ts

@@ -30,3 +30,11 @@ export { OpencodeProvider } from './opencode-provider.js';
 
 // Provider factory
 export { ProviderFactory } from './provider-factory.js';
+
+// Simple query service - unified interface for basic AI queries
+export { simpleQuery, streamingQuery } from './simple-query-service.js';
+export type {
+  SimpleQueryOptions,
+  SimpleQueryResult,
+  StreamingQueryOptions,
+} from './simple-query-service.js';