B4: probe task store, panel API, heartbeat ingestion, agent prober

- probe package: probe_ping_task/probe_ping_node tables; task CRUD
  with hub save semantics (id high-water, base-diff assignment,
  64-per-agent crowding refusal, auto_join cap); filing with
  assignment-gated insert; PingHistory weighted-median chart read
  over minute+hour tiers; auto-join on first Record (ensureRows).
- controller: /panel/api/agent/probe-tasks* management endpoints
  (node id space, hub validation chain verbatim); series=ping now
  serves real rows from probe.PingHistory; heartbeat ingests
  probeResults (missing latency skipped, batch capped); config
  response carries probe_tasks (always present, empty = clear).
- agent: per-task probe loops (immediate first probe, ticker,
  900ms resolve/dial budgets, <=3 addresses, resolve overrun = no
  sample), result buffer drained on heartbeat and requeued on
  failure; task set applied before the config-hash early return.

internal/web/controller/probe_public.go

@@ -120,7 +120,7 @@ func (pc *PublicProbeController) nodes(c *gin.Context) {
 
 type metricsResponse struct {
 	Metrics []probe.MetricRow  `json:"metrics"`
-	Ping    []any              `json:"ping"`
+	Ping    []probe.PingRow    `json:"ping"`
 	Probes  map[string]string  `json:"probes"`
 	Loss    map[string]float64 `json:"loss"`
 	Step    int64              `json:"step"`
@@ -171,12 +171,11 @@ func (pc *PublicProbeController) nodeMetrics(c *gin.Context) {
 	series := c.Query("series")
 	wantMetrics := series == "" || series == "metrics"
 	wantPing := series == "" || series == "ping"
-	_ = wantPing // ping rows are written by B4; until then the series is empty by construction
 
 	span := probe.ComputeSpan(hours, points, time.Now().Unix())
 	resp := metricsResponse{
 		Metrics: []probe.MetricRow{},
-		Ping:    []any{},
+		Ping:    []probe.PingRow{},
 		Probes:  map[string]string{},
 		Loss:    map[string]float64{},
 		Step:    span.Step,
@@ -190,6 +189,25 @@ func (pc *PublicProbeController) nodeMetrics(c *gin.Context) {
 		}
 		resp.Metrics = rows
 	}
+	if wantPing {
+		// B4: the real latency series over the same window/bucket as
+		// the metrics above (hub metrics handler series=ping).
+		pingRows, pingLoss, err := probe.PingHistory(id, span)
+		if err != nil {
+			logger.Warningf("probe public: ping %d: %v", id, err)
+			answerText(c, http.StatusInternalServerError, "服务内部出错")
+			return
+		}
+		names, err := probe.PingTaskNames(id)
+		if err != nil {
+			logger.Warningf("probe public: ping names %d: %v", id, err)
+			answerText(c, http.StatusInternalServerError, "服务内部出错")
+			return
+		}
+		resp.Ping = pingRows
+		resp.Probes = names
+		resp.Loss = pingLoss
+	}
 	c.JSON(http.StatusOK, resp)
 }