Add POST /api/admin/reset-latency endpoint

Zeroes block-update latency counters (count, sum, last, wasted work)
in both memory and the kv store. Used by the StartOS reset-latency
action to let operators start fresh after tuning.

api/internal/state/blocks.go

@@ -113,6 +113,24 @@ func (a *Aggregator) IngestLatencyEvents(ctx context.Context, events <-chan logm
 	}
 }
 
+// ResetLatency zeroes the block-update latency counters both in memory
+// and in the persistent kv store.
+func (a *Aggregator) ResetLatency() {
+	a.mu.Lock()
+	a.latencyCount = 0
+	a.latencySumMs = 0
+	a.latencyLastMs = 0
+	a.staleWorkHashes = 0
+	a.mu.Unlock()
+	if a.Store != nil {
+		_ = a.Store.SetKV(kvLatencyCount, "0")
+		_ = a.Store.SetKV(kvLatencySumMs, "0")
+		_ = a.Store.SetKV(kvLatencyLastMs, "0")
+		_ = a.Store.SetKV(kvStaleWorkHashes, "0")
+	}
+	a.Log.Info("block latency stats reset")
+}
+
 // IngestBlockEvents reads block events from the tailer and appends them
 // to the snapshot's block history. Runs until ctx is cancelled.
 func (a *Aggregator) IngestBlockEvents(ctx context.Context, events <-chan logmon.BlockEvent) {