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.Infrastructure/Persistence/Migrations/20260719021751_AddExtensionRequest.cs

@@ -0,0 +1,28 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace PnvPanel.Infrastructure.Persistence.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddExtensionRequest : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<int>(
+                name: "RequestedDays",
+                table: "SupportTickets",
+                type: "integer",
+                nullable: true);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "RequestedDays",
+                table: "SupportTickets");
+        }
+    }
+}

backend/src/PnvPanel.Infrastructure/Persistence/Migrations/AppDbContextModelSnapshot.cs

@@ -625,6 +625,9 @@ namespace PnvPanel.Infrastructure.Persistence.Migrations
                         .HasMaxLength(100)
                         .HasColumnType("character varying(100)");
 
+                    b.Property<int?>("RequestedDays")
+                        .HasColumnType("integer");
+
                     b.Property<Guid?>("RequestedRoleId")
                         .HasColumnType("uuid");