Improve user auth handling and download monitoring

Adds detection of local users for authentication validation and login, prevents role changes for OIDC users, and clarifies user management UI. Enhances active downloads API to include speed and ETA from qBittorrent, and improves file path handling in download monitoring. Also updates torrent tagging and user info returned by APIs.

src/app/api/admin/settings/route.ts

@@ -15,6 +15,11 @@ export async function GET(request: NextRequest) {
     const configs = await prisma.configuration.findMany();
     const configMap = new Map(configs.map((c) => [c.key, c.value]));
 
+    // Check if any local users exist (for validation)
+    const hasLocalUsers = (await prisma.user.count({
+      where: { authProvider: 'local' }
+    })) > 0;
+
     // Mask sensitive values
     const maskValue = (key: string, value: string | null | undefined) => {
       const sensitiveKeys = ['token', 'api_key', 'password', 'secret'];
@@ -27,6 +32,7 @@ export async function GET(request: NextRequest) {
     // Build response object
     const settings = {
       backendMode: configMap.get('system.backend_mode') || 'plex',
+      hasLocalUsers,
       plex: {
         url: configMap.get('plex_url') || '',
         token: maskValue('token', configMap.get('plex_token')),