GuestLog - User message improvements

- Added UserMessageService to have common methods for showing messages and errors to the user.
- Added Result record so services can return status on operation error (so it can be shown in the UI messages).
- Updated services to use the new Result record.
- Updated pages to use the new IUserMessageService.

src/Somnia.GuestLog/Models/DTOs/Result.cs

@@ -0,0 +1,24 @@
+namespace Somnia.GuestLog.Models.DTOs;
+
+public sealed record Result(bool IsSuccess, string ResultCode, params object[]? Context)
+{
+    public static Result Ok() => new(IsSuccess: true, ResultCode: Models.ResultCode.Ok, Context: null);
+
+    public static Result Fail(string resultCode) => new(IsSuccess: false, resultCode, Context: null);
+    public static Result FailWithContext(string resultCode, params object[] context)
+        => new(IsSuccess: false, resultCode, context);
+    public static Result FailUnknownError()
+        => new(IsSuccess: false, ResultCode: Models.ResultCode.UnknownError, Context: null);
+
+    public bool IsUnknownError => !IsSuccess && ResultCode == Models.ResultCode.UnknownError;
+}
+
+public sealed record Result<T>(bool IsSuccess, T? Value, string ResultCode, params object[]? Context)
+{
+    public static Result<T> Ok(T value) => new(IsSuccess: true, value, ResultCode: Models.ResultCode.Ok, Context: null);
+    public static Result<T> Fail(string resultCode) => new(IsSuccess: false, Value: default, resultCode, Context: null);
+    public static Result<T> FailWithContext(string resultCode, params object[] context)
+        => new(IsSuccess: false, Value: default, resultCode, context);
+
+    public bool IsUnknownError => !IsSuccess && ResultCode == Models.ResultCode.UnknownError;
+}

src/Somnia.GuestLog/Models/ResultCode.cs

@@ -0,0 +1,11 @@
+namespace Somnia.GuestLog.Models;
+
+public static class ResultCode
+{
+    public const string Ok = "Ok";
+    public const string UnknownError = "UnknownError";
+    public const string FailedValidation = "FailedValidation";
+    public const string NotFound = "NotFound";
+
+    public const string GuestCurrentlyInStay = "GuestCurrentlyInStay";
+}