fix: use ssrLoadModule to load Express server in Vite dev plugin

Dynamic import("./server") resolves relative to Vite's .vite-temp/
compilation dir, not the project root. ssrLoadModule resolves from
/app root and processes TypeScript correctly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

vite.config.ts

@@ -42,7 +42,7 @@ function expressPlugin(): Plugin {
     async configureServer(server) {
       try {
         console.log("[Vite] Loading Express server...");
-        const { createServer } = await import("./server");
+        const { createServer } = await server.ssrLoadModule("/server/index.ts");
         const app = createServer();
         console.log("[Vite] Express server created, mounting...");