[FEAT][API] Download a report

## Description
Allow to download a report
## Request

### Method
GET

### URL
/reports/:id/download
### Request Parameters
- id: the report ID, required

### Request Body
None

## Result
### Result parameters
None

### Result Body
The report file

## Example Curl Request

### Request
```
curl -X GET "http://localhost:8080/reports/:id/download"
```

### Curl Response
```
(file content)
```

## Go server

### Struct
```go
type DownloadReportRequest struct {
ID string `json:"id" format:"uuid"`
}
```

### Handler
```go
func (s *Server) handleDownloadReport(w http.ResponseWriter, r *http.Request) {
var req DownloadReportRequest
if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
http.Error(w, err.Error(), http.StatusBadRequest)
return
}

report, err := s.store.GetReport(req.ID)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}

// Serve the report file
w.Header().Set("Content-Type", "application/octet-stream")
w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=%s.pdf", report.Name))
w.Write(report.Data)
}
```
}

w.Header().Set("Content-Type", "application/octet-stream")
w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", report.Name))
if _, err := w.Write(report.Data); err != nil {
http.Error(w, "Internal server error", http.StatusInternalServerError)
return
}
}
```
## Links

- [Reports.download_report](https://github.com/octopize/avatar-python/blob/0.6.2/avatars/api.py#L1048)
- [Any](https://github.com/octopize/avatar-python/blob/0.6.2/avatars/api.py#L1048)

## Automated Issue Details

Dear visitor,

This issue has been automatically generated from the Octopize project [avatar-python](https://github.com/octopize/avatar-python/) to make SIGO compatible. Please vote with a thumbs up or thumbs down to assess the quality of the automatic generation.

Best regards,
The SIGO Team

Start by reading the linked Reports.download_report implementation in avatars/api.py, then locate the Go server's report routes and handleDownloadReport entry point. The work is complete when GET /reports/:id/download retrieves the requested report and returns its file content with the documented download headers.

Written by the indexing model from the issue text.