Add proxy REST endpoint for Estate Reporting API transaction summary

[StuartFerguson]

@## Summary
Add a REST endpoint in TransactionProcessorACL that tunnels through to the Estate Reporting API implementation in the local D:\Projects\TransactionProcessing\EstateReportingAPI codebase.

Target endpoint

• Base route: api/reporting
• Handler group: ReportingEndpoints
• Method: POST
• Route to expose:
  merchantdailyperformancesummary
• Existing upstream alias also present:
  dailymerchaantprformancesummary

Upstream handler

group.MapPost("merchantdailyperformancesummary", ReportingHandlers.GetMerchantDailyPerformanceSummary) .WithStandardProduces<MerchantDailyPerformanceSummaryResponse>();

Example request payload

{
  "merchantReportingId": 12345,
  "startDate": "2026-07-01T00:00:00Z",
  "endDate": "2026-07-01T23:59:59Z"
}

Example response payload

{
  "metrics": [
    {
      "title": "Total Sales Count",
      "value": 6,
      "description": "All sales transactions in the range",
      "category": 0
    },
    {
      "title": "Total Sales Value",
      "value": 123.45,
      "description": "All sales value in the range",
      "category": 1
    },
    {
      "title": "Successful Sales Count",
      "value": 3,
      "description": "Authorised sales count in the range",
      "category": 2
    },
    {
      "title": "Failed Sales Count",
      "value": 3,
      "description": "Declined sales count in the range",
      "category": 4
    },
    {
      "title": "Average Sales Count",
      "value": 6,
      "description": "Average sales count per day in the range",
      "category": 6
    },
    {
      "title": "Average Sales Value",
      "value": 20.57,
      "description": "Average value per sale in the range",
      "category": 7
    },
    {
      "title": "Top Product Sales Count",
      "value": 6,
      "description": "Safaricom Contract Product",
      "category": 8
    }
  ],
  "drillDownTransactions": [
    {
      "reference": "0006",
      "product": "Safaricom Contract Product",
      "status": "Failed",
      "amount": 10.0,
      "transactionDateTime": "2026-07-01T15:00:00Z"
    }
  ]
}

Expected behavior

Expose a matching endpoint in TransactionProcessorACL that forwards requests to the Estate Reporting API transaction summary handler and returns the same response contract.

Implementation notes

• Preserve the request/response shape used by MerchantDailyPerformanceSummary.
• Keep the endpoint path consistent with the reporting routing conventions in TransactionProcessorACL.
• Ensure errors from the downstream API are surfaced clearly.

Acceptance criteria

• A client can call the new endpoint from TransactionProcessorACL.
• The endpoint forwards to the Estate Reporting API transaction summary handler.
• The response matches MerchantDailyPerformanceSummaryResponse.
• Basic success and failure cases are covered by tests if the repo has test coverage for this area.