Implement radar-telemt-dcs aggregation endpoint and UI integration

- Added new API route `/api/agg/radar-telemt-dcs` to aggregate DC status data from multiple upstreams, including metrics like coverage percentage and RTT.
- Implemented handler logic in `handlers.go` and corresponding tests in `handlers_test.go` to ensure correct data retrieval and response formatting.
- Updated the frontend to fetch and display radar DC data, enhancing the user interface with a new section for Telemt ME snapshots.
- Enhanced documentation in `AGGREGATE.md` and `README.md` to reflect the new functionality and usage details.

internal/aggregate/radar_telemt.go

@@ -0,0 +1,44 @@
+package aggregate
+
+import (
+	"context"
+	"net/http"
+	"sort"
+	"sync"
+
+	"github.com/telemt/telemt-api/internal/config"
+)
+
+const statsDcsPath = "stats/dcs"
+
+// FetchRadarTelemtDcs calls GET /v1/stats/dcs on each Telemt in parallel.
+func FetchRadarTelemtDcs(ctx context.Context, client *http.Client, parsed *config.Parsed, aliases []string) RadarTelemtDcsData {
+	if len(aliases) == 0 {
+		return RadarTelemtDcsData{}
+	}
+	rows := make([]RadarTelemtDcsServer, len(aliases))
+	var wg sync.WaitGroup
+	for i, alias := range aliases {
+		i, alias := i, alias
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			data, meta := FetchTelemtGET[DcStatusPayload](ctx, client, parsed, alias, statsDcsPath)
+			row := RadarTelemtDcsServer{
+				Alias:      alias,
+				OK:         meta.OK,
+				HTTPStatus: meta.HTTPStatus,
+				LatencyMs:  meta.LatencyMs,
+				Error:      meta.Error,
+				Revision:   meta.Revision,
+			}
+			if meta.OK {
+				row.Data = &data
+			}
+			rows[i] = row
+		}()
+	}
+	wg.Wait()
+	sort.Slice(rows, func(i, j int) bool { return rows[i].Alias < rows[j].Alias })
+	return RadarTelemtDcsData{Servers: rows}
+}