feat(HAI-002): complete React conversion with build fixes and project setup

- Fix Vite alias to resolve @hai/core to types-only module (avoids Node.js deps in browser bundle)
- Add tsconfig.app.json for client-side typecheck
- Fix server.ts return type annotation
- Update imports to use @hai/core (resolved via Vite alias)
- Add base project files needed for workspace

packages/dashboard/src/server.ts

@@ -7,7 +7,7 @@ import { createSSE } from "./sse.js";
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
 
-export function createServer(store: TaskStore) {
+export function createServer(store: TaskStore): ReturnType<typeof express> {
   const app = express();
 
   app.use(express.json());