CUB-10: Create IMoonrakerClient interface and DTOs

- Expanded IMoonrakerClient interface with 6 strongly-typed methods:
  - GetServerInfoAsync (Moonraker /server/info)
  - IsReachableAsync (connectivity check)
  - GetPrinterInfoAsync (Moonraker /printer/info)
  - GetPrintHistoryAsync (Moonraker /server/history/items)
  - GetPrintStatsAsync (Moonraker /printer/objects/query?print_stats)
  - GetDisplayStatusAsync (Moonraker /printer/objects/query?display_status)
  - GetFilamentUsageAsync (retained for backward compatibility)

- Created Domain/DTOs/Moonraker/ with 7 DTOs:
  - MoonrakerServerInfo, MoonrakerPrinterInfo, MoonrakerPrintJob
  - MoonrakerHistoryResponse, MoonrakerPrintStats
  - MoonrakerDisplayStatus, MoonrakerRequest

- Updated MoonrakerClient implementation to support all new methods
  with proper JSON parsing and mapping helpers

- Full XML doc comments on all public members

backend/Domain/DTOs/Moonraker/MoonrakerDisplayStatus.cs

@@ -0,0 +1,19 @@
+namespace Extrudex.Domain.DTOs.Moonraker;
+
+/// <summary>
+/// Response DTO for Moonraker /printer/objects/query?display_status endpoint.
+/// Contains progress percentage and message for the current print job.
+/// Used by the SignalR hub to push real-time progress to connected clients.
+/// </summary>
+public class MoonrakerDisplayStatus
+{
+    /// <summary>
+    /// Print progress as a decimal between 0 and 1 (0% to 100%).
+    /// </summary>
+    public decimal Progress { get; set; }
+
+    /// <summary>
+    /// Status message displayed on the printer LCD (e.g., "Printing...", "Heating...").
+    /// </summary>
+    public string Message { get; set; } = string.Empty;
+}