fix: forward multipart/form-data correctly in import API proxy

The SvelteKit proxy was calling request.json() unconditionally,
consuming the body before forwarding. File uploads (multipart/form-data)
now use request.formData() and pass the FormData directly to backendFetch
so the fetch API sets the correct Content-Type boundary automatically.

ui/src/lib/paraglide/messages/admin_nav_import.js

@@ -0,0 +1,44 @@
+/* eslint-disable */
+import { getLocale, experimentalStaticLocale } from '../runtime.js';
+
+/** @typedef {import('../runtime.js').LocalizedString} LocalizedString */
+
+/** @typedef {{}} Admin_Nav_ImportInputs */
+
+const en_admin_nav_import = /** @type {(inputs: Admin_Nav_ImportInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Import`)
+};
+
+const ru_admin_nav_import = /** @type {(inputs: Admin_Nav_ImportInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Import`)
+};
+
+const id_admin_nav_import = /** @type {(inputs: Admin_Nav_ImportInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Import`)
+};
+
+const pt_admin_nav_import = /** @type {(inputs: Admin_Nav_ImportInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Import`)
+};
+
+const fr_admin_nav_import = /** @type {(inputs: Admin_Nav_ImportInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Import`)
+};
+
+/**
+* | output |
+* | --- |
+* | "Import" |
+*
+* @param {Admin_Nav_ImportInputs} inputs
+* @param {{ locale?: "en" | "ru" | "id" | "pt" | "fr" }} options
+* @returns {LocalizedString}
+*/
+export const admin_nav_import = /** @type {((inputs?: Admin_Nav_ImportInputs, options?: { locale?: "en" | "ru" | "id" | "pt" | "fr" }) => LocalizedString) & import('../runtime.js').MessageMetadata<Admin_Nav_ImportInputs, { locale?: "en" | "ru" | "id" | "pt" | "fr" }, {}>} */ ((inputs = {}, options = {}) => {
+	const locale = experimentalStaticLocale ?? options.locale ?? getLocale()
+	if (locale === "en") return en_admin_nav_import(inputs)
+	if (locale === "ru") return ru_admin_nav_import(inputs)
+	if (locale === "id") return id_admin_nav_import(inputs)
+	if (locale === "pt") return pt_admin_nav_import(inputs)
+	return fr_admin_nav_import(inputs)
+});

ui/src/routes/api/admin/import/+server.ts

@@ -17,22 +17,41 @@ export const GET: RequestHandler = async ({ locals }) => {
 
 /**
  * POST /api/admin/import
- * Create a new import task.
+ * Create a new import task. Supports both multipart/form-data (file upload)
+ * and application/json (object key reference).
  */
 export const POST: RequestHandler = async ({ request, locals }) => {
 	if (!locals.user || locals.user.role !== 'admin') {
 		throw error(403, 'Forbidden');
 	}
-	const body = await request.json();
-	const res = await backendFetch('/api/admin/import', {
-		method: 'POST',
-		headers: { 'Content-Type': 'application/json' },
-		body: JSON.stringify(body)
-	});
+
+	const ct = request.headers.get('content-type') ?? '';
+
+	let res: Response;
+
+	if (ct.includes('multipart/form-data')) {
+		// Forward the raw FormData body; let the browser-set Content-Type
+		// (which includes the boundary) pass through unchanged.
+		const formData = await request.formData();
+		res = await backendFetch('/api/admin/import', {
+			method: 'POST',
+			// Do NOT set Content-Type manually — the fetch API sets it
+			// automatically with the correct boundary when given a FormData body.
+			body: formData
+		});
+	} else {
+		const body = await request.json();
+		res = await backendFetch('/api/admin/import', {
+			method: 'POST',
+			headers: { 'Content-Type': 'application/json' },
+			body: JSON.stringify(body)
+		});
+	}
+
 	if (!res.ok) {
 		const err = await res.json().catch(() => ({ error: 'Failed to create import task' }));
 		throw error(res.status, err.error || 'Failed to create import task');
 	}
 	const data = await res.json();
 	return json(data);
-};
+};