Fix authentication for download endpoints (fixes #231)

Add missing Authorization header to fetch() calls that bypass the
request() helper. These endpoints returned 401 when auth was enabled
because the JWT token wasn't being sent with the request.

Affected functions in frontend/src/api/client.ts:
- downloadSupportBundle (support bundle download)
- downloadPrinterFilesAsZip (printer file downloads)
- exportArchives (archive CSV/XLSX export)
- exportStats (statistics CSV/XLSX export)

Closes #231

frontend/src/api/client.ts

@@ -2062,9 +2062,13 @@ export const api = {
   getPrinterFileDownloadUrl: (printerId: number, path: string) =>
     `${API_BASE}/printers/${printerId}/files/download?path=${encodeURIComponent(path)}`,
   downloadPrinterFilesAsZip: async (printerId: number, paths: string[]): Promise<Blob> => {
+    const headers: Record<string, string> = { 'Content-Type': 'application/json' };
+    if (authToken) {
+      headers['Authorization'] = `Bearer ${authToken}`;
+    }
     const response = await fetch(`${API_BASE}/printers/${printerId}/files/download-zip`, {
       method: 'POST',
-      headers: { 'Content-Type': 'application/json' },
+      headers,
       body: JSON.stringify({ paths }),
     });
     if (!response.ok) {
@@ -2173,7 +2177,11 @@ export const api = {
     if (options?.dateTo) params.set('date_to', options.dateTo);
     if (options?.search) params.set('search', options.search);
 
-    const response = await fetch(`${API_BASE}/archives/export?${params}`);
+    const headers: Record<string, string> = {};
+    if (authToken) {
+      headers['Authorization'] = `Bearer ${authToken}`;
+    }
+    const response = await fetch(`${API_BASE}/archives/export?${params}`, { headers });
     if (!response.ok) {
       const error = await response.json().catch(() => ({}));
       throw new Error(error.detail || `HTTP ${response.status}`);
@@ -2201,7 +2209,11 @@ export const api = {
     if (options?.printerId) params.set('printer_id', String(options.printerId));
     if (options?.projectId) params.set('project_id', String(options.projectId));
 
-    const response = await fetch(`${API_BASE}/archives/stats/export?${params}`);
+    const headers: Record<string, string> = {};
+    if (authToken) {
+      headers['Authorization'] = `Bearer ${authToken}`;
+    }
+    const response = await fetch(`${API_BASE}/archives/stats/export?${params}`, { headers });
     if (!response.ok) {
       const error = await response.json().catch(() => ({}));
       throw new Error(error.detail || `HTTP ${response.status}`);
@@ -3945,7 +3957,11 @@ export const supportApi = {
     }),
 
   downloadSupportBundle: async () => {
-    const response = await fetch(`${API_BASE}/support/bundle`);
+    const headers: Record<string, string> = {};
+    if (authToken) {
+      headers['Authorization'] = `Bearer ${authToken}`;
+    }
+    const response = await fetch(`${API_BASE}/support/bundle`, { headers });
     if (!response.ok) {
       const error = await response.json().catch(() => ({}));
       throw new Error(error.detail || `HTTP ${response.status}`);