Feat(admin/currencies): add CurrencyRate field and bulk rate update

[suatsuphi]

• Introduced CurrencyRate property in ExchangeRate and CurrencyModel
• Updated CurrencyController logic to handle CurrencyRate recalculation with epsilon tolerance
• Added ApplyRatesToAllCurrencies action for live bulk rate updates
• Extended admin grid views (_Grid.Currencies, _Grid.LiveRates) to display and edit CurrencyRate
• Included confirm prompt and toolbar button for bulk rate application

Language resource additions for currency rate updates
Admin.Configuration.Currencies.ApplyRatesToAll → Action key for applying exchange rates to all currencies.

Admin.Configuration.Currencies.Q_ApplyRatesToAll → Confirmation message key: “Exchange rates will be applied to all currencies. Do you want to continue?”

Admin.Configuration.Currencies.Fields.CurrencyRate → Field label key for displaying the conversion currency rate.

/// <summary>
/// **The conversion currency rate of this currency from the base currency**
/// </summary>
public decimal CurrencyRate { get; set; } = 1.0m;

/// <summary>
/// **The conversion rate of this currency from the base currency**
/// </summary>
public decimal Rate { get; set; } = 1.0m;

• The Central Bank of Turkey publishes exchange rates on a daily basis. It does not provide rates!
  model.CurrencyRate = model.Rate == 0 ? 0 : 1.0M / model.Rate;

• The Currency Rate can be saved on the _Grid.Currencies.cshtml page... If a Currency Rate has been entered, the rate can be calculated.

Code - CurrencyUpdate

[HttpPost]
[Permission(Permissions.Configuration.Currency.Update)]
public async Task<IActionResult> CurrencyUpdate(CurrencyModel model)
{
    var success = false;
    var currency = await _db.Currencies.FindByIdAsync(model.Id);

    if (currency != null)
    {
        try
        {
            **
            decimal exchangeRate = currency.Rate == 0 ? 0 : 1.0M / currency.Rate;
            const decimal epsilon = 0.00000001M; // builder.Property(c => c.Rate).HasPrecision(18, 8);
            if (Math.Abs(model.CurrencyRate - exchangeRate) > epsilon)
            {
                model.Rate = 1.0M / model.CurrencyRate;
            }
            **

            await MapperFactory.MapAsync(model, currency);
            await _db.SaveChangesAsync();
            success = true;
        }
        catch (Exception ex)
        {
            NotifyError(ex);
        }
    }

    return Json(new { success });
}

• You can save the rates to the 'Currencies' section as 'Live currency rates' using the 'Apply rates to all' button.

Code - ApplyRatesToAllCurrencies

```

    [HttpPost]
    [Permission(Permissions.Configuration.Currency.EditExchangeRate)]
    public async Task<IActionResult> ApplyRatesToAllCurrencies(GridCommand command)
    {
        List<ExchangeRate> rates = (await Services.CurrencyService
            .GetCurrencyLiveRatesAsync(!command.InitialRequest))
            .ToList();

        var currencies = await _db.Currencies.ToListAsync();

        foreach (var currency in currencies)
        {
            var rateInfo = rates.FirstOrDefault(r => r.CurrencyCode == currency.CurrencyCode);
            if (rateInfo != null && rateInfo.Rate > 0)
            {
                currency.Rate = rateInfo.Rate;
                currency.UpdatedOnUtc = DateTime.UtcNow;
            }
        }

        await _db.SaveChangesAsync();
        NotifySuccess(T("Admin.Common.TaskSuccessfullyProcessed"));
        return RedirectToAction(nameof(Index));
    }

</details>

[mgesing]

Why is ApplyRatesToAllCurrencies necessary? What benefit does it provide? It seems to do the same thing as UpdateExchangeRateTask.

[suatsuphi]

The user doesn’t want to update exchange rates automatically. If they want to update the rates on that particular day, they have to go to TASK, find ‘Update Currencies’ and run it manually. There is no 'Update Exchange Rate' button in the exchange rate section - just one by one