feat(print): dashboard UI for print servers + auto-discovered printer pickers

Phase 4 (final). Settings → Printers now has a "Print servers" section: add a
print server (issues a one-time pairing code with steps), see each agent's online
status, its auto-discovered printers, test any of them, and revoke. Receipt,
kitchen and per-station printers can now be picked from a dropdown of discovered
devices instead of typing an IP (manual IP stays as fallback). Wires the device
mappings through the branch print-settings + kitchen-station DTOs/services and adds
the device-test endpoint. fa/en/ar strings added.

Completes the cloud↔LAN print-agent feature (entities/hub → routing → agent → UI).
Remaining polish: agent system-tray + run-at-login + installer, optional LAN scan.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Meezi.API/Controllers/BranchPrintSettingsController.cs

@@ -91,6 +91,14 @@ public class BranchPrintSettingsController : CafeApiControllerBase
                 : request.PosDeviceIp.Trim();
         if (request.PosDevicePort.HasValue)
             branch.PosDevicePort = request.PosDevicePort.Value;
+        if (request.ReceiptPrintDeviceId is not null)
+            branch.ReceiptPrintDeviceId = string.IsNullOrWhiteSpace(request.ReceiptPrintDeviceId)
+                ? null
+                : request.ReceiptPrintDeviceId;
+        if (request.KitchenPrintDeviceId is not null)
+            branch.KitchenPrintDeviceId = string.IsNullOrWhiteSpace(request.KitchenPrintDeviceId)
+                ? null
+                : request.KitchenPrintDeviceId;
 
         branch.UpdatedAt = DateTime.UtcNow;
         await _db.SaveChangesAsync(ct);
@@ -110,5 +118,7 @@ public class BranchPrintSettingsController : CafeApiControllerBase
         b.ReceiptFooter,
         b.WifiPassword,
         b.PosDeviceIp,
-        b.PosDevicePort);
+        b.PosDevicePort,
+        b.ReceiptPrintDeviceId,
+        b.KitchenPrintDeviceId);
 }