feat(templates): add localized push templates and actions

Share template keys across email and push with independent editors and revisions. Render localized actions and preserve version-one delivery.

Ref: IT-1627

HrynCo.NotificationService.Worker.Services/Push/PushChannelTestMessage.cs

@@ -0,0 +1,31 @@
+using HrynCo.NotificationService.DAL.Abstract.Templates;
+
+namespace HrynCo.NotificationService.Worker.Services.Push;
+
+public sealed record PushChannelTestMessage
+{
+    public required string Token { get; init; }
+    public int Version { get; init; } = 1;
+    public Guid? BindingId { get; init; }
+    public string? ActionKey { get; init; }
+    public string? ButtonLabel { get; init; }
+
+    public string? Validate()
+    {
+        if (!PushMessageValidator.IsSupportedVersion(Version)) return "Unsupported push payload version. Supported versions are 1 and 2.";
+        if (string.IsNullOrWhiteSpace(Token) || Token.Length > 4096 || Token.Any(char.IsWhiteSpace))
+            return "Enter a valid recipient FCM token.";
+        if (Version == 1) return null;
+        if (BindingId is null || BindingId == Guid.Empty) return "Enter the device's current binding ID for the button-format test.";
+        try
+        {
+            PushTemplateActionValidation.Validate(new PushTemplateActions
+            {
+                DefaultAction = ActionKey,
+                Buttons = [new PushTemplateButton { Action = ActionKey!, Label = ButtonLabel! }]
+            });
+            return null;
+        }
+        catch (EmailTemplateWriteException) { return "Enter a valid action key and a button label (1–100 characters)."; }
+    }
+}