Refactor pricing endpoints and enhance support for pricing retrieval

- Added a new endpoint `/api/support/pricing` to allow users to retrieve pricing information, making it accessible for role request dialogs.
- Introduced the `GetSupportPricing` method to handle pricing queries, ensuring that pricing data is available to non-admin users.
- Updated frontend components to integrate the new pricing retrieval functionality, displaying estimated costs based on user-selected configurations.
- Removed the `PricingSettingsDto` as it is no longer needed, streamlining the pricing data structure.
- Enhanced API documentation to reflect the new endpoint and its usage in the support context.

backend/src/PnvPanel.Application/Common/Interfaces/PricingSettingsDto.cs

@@ -0,0 +1,20 @@
+using PnvPanel.Domain.Pricing;
+
+namespace PnvPanel.Application.Common.Interfaces;
+
+/// <summary>Все поля — цена за конфиг В МЕСЯЦ при соответствующем тарифе оплаты; итог за период =
+/// ставка × число месяцев. Используется и Admin (редактирование), и Support (справка при заявке на
+/// роль) — см. PricingSettingsDto.FromDomain.</summary>
+public sealed record PricingSettingsDto(
+    int? PricePerConfigPerQuarter,
+    int? PricePerConfigPerHalfYear,
+    int? PricePerConfigPerYear
+)
+{
+    public static PricingSettingsDto FromDomain(PricingSettings settings) =>
+        new(
+            settings.PricePerConfigPerQuarter,
+            settings.PricePerConfigPerHalfYear,
+            settings.PricePerConfigPerYear
+        );
+}