P8(1): restore homepage overview curves on a memory-only sampling ring

Backend: new overviewMetrics store — a single-tier (2s x 360 = 12min)
in-memory ring fed by ServerService.RefreshStatus for exactly the eight
overview series (cpu/mem/swap/diskUsage/netUp/netDown/tcpCount/udpCount).
No persistence, no gob snapshot, no system-history page: the only surface
is GET /panel/api/server/history/:metric/:bucket restricted to those
keys, which seeds the frontend curves. ~46KB bounded by construction;
the ring starts empty on every panel start.

Frontend: restore useOverviewHistory + the VitalTile/ThroughputCard/
ConnectionsCard sparklines and the IndexPage wiring exactly as they
were before P7 removed them along with the history module.

internal/web/controller/server.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"net/http"
 	"regexp"
+	"slices"
 	"strconv"
 
 	"github.com/mhsanaei/3x-ui/v3/internal/database/model"
@@ -39,6 +40,7 @@ func NewServerController(g *gin.RouterGroup) *ServerController {
 // initRouter sets up the routes for server status, Xray management, and utility endpoints.
 func (a *ServerController) initRouter(g *gin.RouterGroup) {
 	g.GET("/status", a.status)
+	g.GET("/history/:metric/:bucket", a.getOverviewHistoryBucket)
 	g.GET("/getPanelUpdateInfo", a.getPanelUpdateInfo)
 	g.GET("/getUpdateStatus", a.getUpdateStatus)
 	g.GET("/getConfigJson", a.getConfigJson)
@@ -86,6 +88,25 @@ func (a *ServerController) startTask() {
 // status returns the current server status information.
 func (a *ServerController) status(c *gin.Context) { jsonObj(c, a.serverService.LastStatus(), nil) }
 
+// getOverviewHistoryBucket returns up to 60 buckets of one homepage
+// overview metric (see service.OverviewMetricKeys). It backs only the
+// index-page sparkline seed; the store behind it is the memory-only
+// overview ring — not the removed system-history API (no other metrics,
+// no persistence, nothing to browse beyond the overview window).
+func (a *ServerController) getOverviewHistoryBucket(c *gin.Context) {
+	metric := c.Param("metric")
+	if !slices.Contains(service.OverviewMetricKeys, metric) {
+		jsonMsg(c, "invalid metric", fmt.Errorf("unknown metric"))
+		return
+	}
+	bucket, err := strconv.Atoi(c.Param("bucket"))
+	if err != nil || bucket <= 0 || !service.IsAllowedHistoryBucket(bucket) {
+		jsonMsg(c, "invalid bucket", fmt.Errorf("unsupported bucket"))
+		return
+	}
+	jsonObj(c, a.serverService.AggregateOverviewMetric(metric, bucket, 60), nil)
+}
+
 func (a *ServerController) getFail2banStatus(c *gin.Context) {
 	jsonObj(c, a.serverService.GetFail2banStatus(), nil)
 }