Fix frontend API calls missing auth tokens

Several frontend components were using raw fetch() instead of the API
client, causing 401 Unauthorized errors when authentication is enabled.

Changes:
- SpoolmanSettings: Use api.getSpoolmanSettings/updateSpoolmanSettings
- ProjectsPage: Use api.importProjectFile for ZIP imports
- ProjectDetailPage: Use api.exportProjectZip for exports
- CameraPage/EmbeddedCameraViewer: Use api.getCameraStatus

Added to API client:
- getSpoolmanSettings()
- updateSpoolmanSettings()
- importProjectFile()
- exportProjectZip()
- getCameraStatus()

Added tests for auth token handling in client.test.ts
Fixed VirtualPrinterSettings test expectations to match i18n strings

Closes #231

frontend/src/components/EmbeddedCameraViewer.tsx

@@ -184,17 +184,14 @@ export function EmbeddedCameraViewer({ printerId, printerName, viewerIndex = 0,
 
     stallCheckIntervalRef.current = setInterval(async () => {
       try {
-        const response = await fetch(`/api/v1/printers/${printerId}/camera/status`);
-        if (response.ok) {
-          const status = await response.json();
-          if (status.stalled || (!status.active && !streamError)) {
-            if (stallCheckIntervalRef.current) {
-              clearInterval(stallCheckIntervalRef.current);
-              stallCheckIntervalRef.current = null;
-            }
-            setStreamLoading(false);
-            attemptReconnect();
+        const status = await api.getCameraStatus(printerId);
+        if (status.stalled || (!status.active && !streamError)) {
+          if (stallCheckIntervalRef.current) {
+            clearInterval(stallCheckIntervalRef.current);
+            stallCheckIntervalRef.current = null;
           }
+          setStreamLoading(false);
+          attemptReconnect();
         }
       } catch {
         // Ignore errors

frontend/src/components/SpoolmanSettings.tsx

@@ -6,32 +6,6 @@ import type { SpoolmanSyncResult, Printer } from '../api/client';
 import { Card, CardContent, CardHeader } from './Card';
 import { Button } from './Button';
 
-interface SpoolmanSettingsData {
-  spoolman_enabled: string;
-  spoolman_url: string;
-  spoolman_sync_mode: string;
-}
-
-async function getSpoolmanSettings(): Promise<SpoolmanSettingsData> {
-  const response = await fetch('/api/v1/settings/spoolman');
-  if (!response.ok) {
-    throw new Error('Failed to load Spoolman settings');
-  }
-  return response.json();
-}
-
-async function updateSpoolmanSettings(data: Partial<SpoolmanSettingsData>): Promise<SpoolmanSettingsData> {
-  const response = await fetch('/api/v1/settings/spoolman', {
-    method: 'PUT',
-    headers: { 'Content-Type': 'application/json' },
-    body: JSON.stringify(data),
-  });
-  if (!response.ok) {
-    throw new Error('Failed to save Spoolman settings');
-  }
-  return response.json();
-}
-
 export function SpoolmanSettings() {
   const queryClient = useQueryClient();
   const [localEnabled, setLocalEnabled] = useState(false);
@@ -45,7 +19,7 @@ export function SpoolmanSettings() {
   // Fetch Spoolman settings
   const { data: settings, isLoading: settingsLoading } = useQuery({
     queryKey: ['spoolman-settings'],
-    queryFn: getSpoolmanSettings,
+    queryFn: api.getSpoolmanSettings,
   });
 
   // Fetch Spoolman status
@@ -93,7 +67,7 @@ export function SpoolmanSettings() {
   // Save mutation
   const saveMutation = useMutation({
     mutationFn: () =>
-      updateSpoolmanSettings({
+      api.updateSpoolmanSettings({
         spoolman_enabled: localEnabled ? 'true' : 'false',
         spoolman_url: localUrl,
         spoolman_sync_mode: localSyncMode,