Implement extension request and gift functionalities in billing system

- Added new endpoints for creating and managing extension requests, allowing users to request billing period extensions.
- Implemented admin approval processes for extension requests via Telegram, including inline buttons for approval and rejection.
- Introduced a gifting feature for admins to grant additional billing days directly to users without a request.
- Updated the support ticket model to accommodate extension requests and their associated properties.
- Enhanced the Telegram notifier to inform admins of new extension requests and notify users of approval or rejection.
- Updated frontend components to support the new extension request and gifting functionalities, including user interfaces for managing these features.
- Revised API documentation to reflect the new endpoints and their usage in the billing context.

backend/src/PnvPanel.Application/Support/TicketDetailDto.cs

@@ -5,6 +5,7 @@ namespace PnvPanel.Application.Support;
 /// <summary>
 /// RequestedRoleName — имя существующей роли, если RequestedRoleId задан (резолвится хендлером,
 /// на SupportTicket хранится только Id). Для новой роли имя лежит прямо в ProposedRoleName.
+/// RequestedDays — только для ExtensionRequest (продление оплаченного периода).
 /// </summary>
 public sealed record TicketDetailDto(
     Guid Id,
@@ -17,6 +18,7 @@ public sealed record TicketDetailDto(
     string? ProposedRoleName,
     int? ProposedMaxConfigs,
     int? ProposedMaxIpLimit,
+    int? RequestedDays,
     DateTimeOffset CreatedAt,
     IReadOnlyList<TicketCommentDto> Comments
 );