build(docs): set build.target = 'modules'

Explicility set the `build.target` to `modules`, as Vite v7 changes this
and drops support for older browsers.

We probably should do this eventually too, but maybe as part of a
Mermaid v12 release.

packages/mermaid/src/docs/vite.config.ts

@@ -13,6 +13,10 @@ const virtualModuleId = 'virtual:mermaid-config';
 const resolvedVirtualModuleId = '\0' + virtualModuleId;
 
 export default defineConfig({
+  build: {
+    // Vite v7 changes the default target and drops old browser support
+    target: 'modules',
+  },
   optimizeDeps: {
     // vitepress is aliased with replacement `join(DIST_CLIENT_PATH, '/index')`
     // This needs to be excluded from optimization