fix(config): resolve default server assets dir from serverDir (#4562)

Author: danielroe

docs/1.docs/50.assets.md

@@ -113,7 +113,7 @@ export default defineConfig({
 
 ## Server Assets
 
-All assets in `assets/` directory will be added to the server bundle. After building your application, you can find them in the `.output/server/chunks/raw/` directory. Be careful with the size of your assets, as they will be bundled with the server bundle.
+All assets in the `assets/` directory (relative to [`serverDir`](/config#serverdir) when it is set, otherwise the project root) will be added to the server bundle. After building your application, you can find them in the `.output/server/chunks/raw/` directory. Be careful with the size of your assets, as they will be bundled with the server bundle.
 
 > [!TIP]
 > Unless using `useStorage()`, assets won't be included in the server bundle.

src/config/resolvers/assets.ts

@@ -28,10 +28,10 @@ export async function resolveAssetsOptions(options: NitroOptions) {
   for (const serverAsset of options.serverAssets) {
     serverAsset.dir = resolve(options.rootDir, serverAsset.dir);
   }
-  // 2. Add server/ directory
+  // 2. Add <serverDir>/assets directory
   options.serverAssets.push({
     baseName: "server",
-    dir: resolve(options.rootDir, "assets"),
+    dir: resolve(options.serverDir || options.rootDir, "assets"),
   });
 
   // Infer `fallthrough` and `maxAge` from publicAssets