Fix SSR: align @modern-js/runtime to v2.70.8 and re-enable stream SSR

The server build was failing with "window is not defined" during SSR because
@modern-js/runtime@3.1.3 had an SSR-unsafe window reference in its router
plugin. Pinning runtime to 2.70.8 (matching app-tools) resolves the version
mismatch and eliminates the server-side window access.

modern.config.ts

@@ -12,7 +12,11 @@ export default defineConfig({
   runtime: {
     router: true,
   },
-  server: {},  // SSR disabled temporarily to debug client-side rendering
+  server: {
+    ssr: {
+      mode: "stream",
+    },
+  },
   output: {
     distPath: { root: isRemote ? "dist/remote" : "dist/standalone" },
   },

package.json

@@ -23,7 +23,7 @@
   "dependencies": {
     "@microsoft/signalr": "^10.0.0",
     "@modern-js/app-tools": "2.70.8",
-    "@modern-js/runtime": "^3.1.3",
+    "@modern-js/runtime": "2.70.8",
     "@module-federation/enhanced": "2.3.2",
     "@module-federation/modern-js": "2.3.2",
     "@opentelemetry/api": "^1.9.1",