Add security blocklist for dangerous admin endpoints

- Block system restart/shutdown endpoints
- Block system configuration changes
- Block plugin management (install/uninstall/configure)
- Block scheduled task management
- Block server startup/setup endpoints
- Block user creation endpoint
- Block library management (refresh, virtual folders)
- Block server logs and activity log access
- Log blocked attempts with IP address for security monitoring
- Returns 403 Forbidden with descriptive error message

This maintains client compatibility via catch-all proxy while preventing
unauthorized access to administrative functions.

allstarr/Controllers/JellyfinController.cs

@@ -1662,6 +1662,7 @@ public class JellyfinController : ControllerBase
     /// <summary>
     /// Catch-all endpoint that proxies unhandled requests to Jellyfin transparently.
     /// This route has the lowest priority and should only match requests that don't have SearchTerm.
+    /// Blocks dangerous admin endpoints for security.
     /// </summary>
     [HttpGet("{**path}", Order = 100)]
     [HttpPost("{**path}", Order = 100)]
@@ -1670,6 +1671,39 @@ public class JellyfinController : ControllerBase
         // DEBUG: Log EVERY request to see what's happening
         _logger.LogWarning("ProxyRequest called with path: {Path}", path);
         
+        // Block dangerous admin endpoints
+        var blockedPrefixes = new[]
+        {
+            "system/restart",           // Server restart
+            "system/shutdown",          // Server shutdown
+            "system/configuration",     // System configuration changes
+            "system/logs",              // Server logs access
+            "system/activitylog",       // Activity log access
+            "plugins/",                 // Plugin management (install/uninstall/configure)
+            "scheduledtasks/",          // Scheduled task management
+            "startup/",                 // Initial server setup
+            "users/new",                // User creation
+            "library/refresh",          // Library scan (expensive operation)
+            "library/virtualfolders",   // Library folder management
+            "branding/",                // Branding configuration
+            "displaypreferences/",      // Display preferences (if not user-specific)
+            "notifications/admin"       // Admin notifications
+        };
+        
+        // Check if path matches any blocked prefix
+        if (blockedPrefixes.Any(prefix => 
+            path.StartsWith(prefix, StringComparison.OrdinalIgnoreCase)))
+        {
+            _logger.LogWarning("BLOCKED: Access denied to admin endpoint: {Path} from {IP}", 
+                path, 
+                HttpContext.Connection.RemoteIpAddress);
+            return StatusCode(403, new 
+            { 
+                error = "Access to administrative endpoints is not allowed through this proxy",
+                path = path
+            });
+        }
+        
         // Intercept Spotify playlist requests by ID
         if (_spotifySettings.Enabled && 
             path.StartsWith("playlists/", StringComparison.OrdinalIgnoreCase) &&