Fix JWT sub claim to carry the actual user ID

The sub claim was hardcoded to the literal string "TokenForTheApiWithAuth"
for every token, making it useless for identifying the principal. It now
holds user.Id, matching the JWT spec and enabling standard token inspection
and future revocation workflows.

Marechai.Server/Services/TokenService.cs

@@ -64,7 +64,7 @@ public sealed class TokenService(IConfiguration configuration)
         {
             List<Claim> claims =
             [
-                new(JwtRegisteredClaimNames.Sub, "TokenForTheApiWithAuth"),
+                new(JwtRegisteredClaimNames.Sub, user.Id),
                 new(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),
                 new(JwtRegisteredClaimNames.Iat,
                     EpochTime.GetIntDate(DateTime.UtcNow).ToString(CultureInfo.InvariantCulture)),