Add button and custom modal flow implemented

lib/server/uploads/uploadRoot.ts

@@ -0,0 +1,16 @@
+import { mkdir } from "node:fs/promises";
+import path from "node:path";
+
+/**
+ * Directory for persisted user uploads (Cloudron localstorage mount in prod).
+ * When unset, upload routes return `server_misconfigured`.
+ */
+export function getUploadRootFromEnv(): string | null {
+  const raw = process.env.UPLOAD_ROOT?.trim();
+  if (!raw) return null;
+  return path.resolve(raw);
+}
+
+export async function ensureUploadRootExists(root: string): Promise<void> {
+  await mkdir(root, { recursive: true });
+}