Add cost service for per-VIN cost estimation

- Estimates cloud vs on-prem costs per active vehicle
- Queries feature_table_last_shard from ClickHouse (lightweight)
- 85% savings estimate with on-prem (hardware only)
- Deployed to cec-prd-cluster-1 (internal only)
- Text report endpoint at /cost/report

services/cost/handlers/handlers.go

@@ -2,6 +2,7 @@ package handlers
 
 import (
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"strconv"
 	"strings"
@@ -185,3 +186,82 @@ func respondJSON(w http.ResponseWriter, data interface{}) {
 		logger.Error().Err(err).Msg("Failed to encode JSON response")
 	}
 }
+
+// GetReport returns a plain text cost report
+// GET /cost/report
+func GetReport(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	to := time.Now()
+	from := to.AddDate(0, -1, 0) // Last month
+
+	summary, err := services.GetFleetCostSummary(from, to, 10)
+	if err != nil {
+		logger.Error().Err(err).Msg("Failed to get report data")
+		http.Error(w, "Failed to get report data", http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("Content-Type", "text/plain")
+
+	report := `
+╔══════════════════════════════════════════════════════════════════╗
+║                    COST SERVICE REPORT                           ║
+╠══════════════════════════════════════════════════════════════════╣
+║  Period: %s to %s
+╠══════════════════════════════════════════════════════════════════╣
+║  FLEET OVERVIEW                                                  ║
+║  ─────────────────────────────────────────────────────────────── ║
+║  Active Vehicles:     %d                                         
+║  Cloud Cost:          $%.2f                                      
+║  On-Prem Cost:        $%.2f                                      
+║  Savings:             $%.2f (%.1f%%)                             
+╠══════════════════════════════════════════════════════════════════╣
+║  COST RATES                                                      ║
+║  ─────────────────────────────────────────────────────────────── ║
+║  Cloud:   CPU $%.3f/core-hr   Memory $%.4f/GB-hr                 
+║  On-Prem: CPU $%.3f/core-hr   Memory $%.4f/GB-hr                 
+╠══════════════════════════════════════════════════════════════════╣
+║  ANNUAL PROJECTION (based on current usage)                      ║
+║  ─────────────────────────────────────────────────────────────── ║
+║  Cloud Annual:        $%.2f                                      
+║  On-Prem Annual:      $%.2f                                      
+║  Annual Savings:      $%.2f                                      
+╚══════════════════════════════════════════════════════════════════╝
+`
+	annualCloud := summary.TotalCloudCost * 12
+	annualOnprem := summary.TotalOnpremCost * 12
+	annualSavings := annualCloud - annualOnprem
+
+	fmt.Fprintf(w, report,
+		from.Format("2006-01-02"), to.Format("2006-01-02"),
+		summary.VehicleCount,
+		summary.TotalCloudCost,
+		summary.TotalOnpremCost,
+		summary.TotalSavings, summary.SavingsPercent,
+		services.CloudCPUPerCoreHour, services.CloudMemoryPerGBHour,
+		services.OnpremCPUPerCoreHour, services.OnpremMemoryPerGBHour,
+		annualCloud, annualOnprem, annualSavings,
+	)
+
+	// Add top cost VINs if any
+	if len(summary.TopCostVins) > 0 {
+		fmt.Fprintf(w, "\nTOP COST VEHICLES:\n")
+		fmt.Fprintf(w, "%-20s %12s %12s %10s\n", "VIN", "Cloud $", "On-Prem $", "Savings %")
+		fmt.Fprintf(w, "%-20s %12s %12s %10s\n", "───────────────────", "──────────", "──────────", "────────")
+		for _, v := range summary.TopCostVins {
+			fmt.Fprintf(w, "%-20s %12.2f %12.2f %9.1f%%\n",
+				truncateVIN(v.VIN), v.TotalCloudCost, v.TotalOnpremCost, v.SavingsPercent)
+		}
+	}
+}
+
+func truncateVIN(vin string) string {
+	if len(vin) > 20 {
+		return vin[:17] + "..."
+	}
+	return vin
+}