docs: add troubleshooting for index.html error (#12365)

www/apps/resources/app/troubleshooting/_sections/admin/build-error.mdx

@@ -0,0 +1,17 @@
+If you get the following error when you start the Medusa application, typically in production:
+
+```bash
+Could not find index.html in the admin build directory. Make sure to run 'medusa build' before starting the server.
+```
+
+## Why this Error Occurred
+
+This error occurs if you didn't follow the build process correctly. For example, you don't have an `.env.production` file or you ran the `start` command outside the `.medusa/server` directory.
+
+---
+
+## How to Fix it
+
+To fix this error, make sure you follow the build process correctly as explained in the [Build](!docs!/learn/build) documentation.
+
+You can also follow the [General Deployment](!docs!/learn/deployment/general) documentation if you're facing this error in your deployed application. This guide gives you the general steps to follow when deploying your Medusa application.

www/apps/resources/app/troubleshooting/medusa-admin/build-error/page.mdx

@@ -0,0 +1,9 @@
+import BuildError from "../../_sections/admin/build-error.mdx"
+
+export const metadata = {
+  title: `Could not find index.html Error`,
+}
+
+# {metadata.title}
+
+<BuildError />

www/apps/resources/generated/edit-dates.mjs

@@ -6218,5 +6218,6 @@ export const generatedEditDates = {
   "references/module_events/module_events.Region/page.mdx": "2025-05-01T15:18:45.934Z",
   "references/module_events/module_events.Sales_Channel/page.mdx": "2025-05-01T15:18:45.933Z",
   "references/module_events/module_events.User/page.mdx": "2025-05-01T15:18:45.932Z",
-  "references/modules/module_events/page.mdx": "2025-05-01T15:18:45.930Z"
+  "references/modules/module_events/page.mdx": "2025-05-01T15:18:45.930Z",
+  "app/troubleshooting/medusa-admin/build-error/page.mdx": "2025-05-05T15:56:02.042Z"
 }

www/apps/resources/generated/files-map.mjs

@@ -1319,6 +1319,10 @@ export const filesMap = [
     "filePath": "/www/apps/resources/app/troubleshooting/medusa-admin/blocked-request/page.mdx",
     "pathname": "/troubleshooting/medusa-admin/blocked-request"
   },
+  {
+    "filePath": "/www/apps/resources/app/troubleshooting/medusa-admin/build-error/page.mdx",
+    "pathname": "/troubleshooting/medusa-admin/build-error"
+  },
   {
     "filePath": "/www/apps/resources/app/troubleshooting/medusa-admin/no-widget-route/page.mdx",
     "pathname": "/troubleshooting/medusa-admin/no-widget-route"

www/apps/resources/generated/generated-troubleshooting-sidebar.mjs

@@ -248,6 +248,14 @@ const generatedgeneratedTroubleshootingSidebarSidebar = {
           "path": "/troubleshooting/medusa-admin/blocked-request",
           "title": "Blocked Request",
           "children": []
+        },
+        {
+          "loaded": true,
+          "isPathHref": true,
+          "type": "link",
+          "path": "/troubleshooting/medusa-admin/build-error",
+          "title": "index.html Error",
+          "children": []
         }
       ]
     },

www/apps/resources/sidebars/troubleshooting.mjs

@@ -166,6 +166,11 @@ export const troubleshootingSidebar = [
         path: "/troubleshooting/medusa-admin/blocked-request",
         title: "Blocked Request",
       },
+      {
+        type: "link",
+        path: "/troubleshooting/medusa-admin/build-error",
+        title: "index.html Error",
+      },
     ],
   },
   {