Add inbound country flags and node load in location picker

- Inbound.CountryCode (ISO alpha-2), set on publish; flag shown before
  the location name (SVG via country-flag-icons on the site, emoji in bot)
- Node.Capacity (optional, not a limit); available inbounds report load
  percent of capacity or active config count, sorted least loaded first

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/tests/PnvPanel.Application.Tests/Admin/Nodes/UpdateNodeCommandHandlerTests.cs

@@ -40,6 +40,7 @@ public class UpdateNodeCommandHandlerTests
             true,
             false,
             null,
+            null,
             null
         );
 
@@ -69,6 +70,7 @@ public class UpdateNodeCommandHandlerTests
             true,
             false,
             null,
+            null,
             null
         );
 
@@ -90,7 +92,7 @@ public class UpdateNodeCommandHandlerTests
 
         var handler = new UpdateNodeCommandHandler(dbContext, _gateway, _secretProtector, _currentUser);
 
-        var command = new UpdateNodeCommand(node.Id, "node-1", "not-a-uri", null, true, false, null, null);
+        var command = new UpdateNodeCommand(node.Id, "node-1", "not-a-uri", null, true, false, null, null, null);
 
         var result = await handler.Handle(command, CancellationToken.None);
 
@@ -121,6 +123,7 @@ public class UpdateNodeCommandHandlerTests
             true,
             false,
             null,
+            null,
             null
         );
 
@@ -152,7 +155,8 @@ public class UpdateNodeCommandHandlerTests
             true,
             false,
             "new-admin",
-            "new-password"
+            "new-password",
+            null
         );
 
         var result = await handler.Handle(command, CancellationToken.None);
@@ -181,6 +185,7 @@ public class UpdateNodeCommandHandlerTests
             true,
             false,
             "new-admin",
+            null,
             null
         );
 
@@ -211,6 +216,7 @@ public class UpdateNodeCommandHandlerTests
             true,
             true,
             null,
+            null,
             null
         );
 
@@ -235,6 +241,7 @@ public class UpdateNodeCommandHandlerTests
             true,
             false,
             null,
+            null,
             null
         );