Merchant daily performance response drops the new Type field

[StuartFerguson]

The PR adds Type to MetricItem in EstateReportingAPI.Models/MerchantDailyPerformanceSummaryRequest.cs, but the handler does not project it into the API response.

Impact:

• Clients still only receive Category
• The new identifier is effectively unusable outside the business layer

Suggested fix:

• Add Type to the public DTO path and map it in EstateReportingAPI/Handlers/TransactionHandler.cs.