Add block-update latency tracking, raw share counters, and shares bar UI

Log ZMQ→mining.notify latency in ckpool (patch 0005), expose a raw
reject counter (patch 0006), and surface both in the dashboard:

- Block latency card shows avg/last ms, wasted work, and block count
- SharesBar component shows session + all-time accepted/rejected with
  a Demon Slayer flame-slash animation on new shares
- Miners card info moved to MinersTable section header
- Latency stats and share counts persist across restarts via kv store
- Removed misleading pool-wide share stats from per-worker/user pages
  (ckpool doesn't expose per-user raw counts)

api/internal/ckpool/types.go

@@ -26,6 +26,7 @@ type PoolStats struct {
 	SPS60        float64 `json:"sps60"`
 	Accepted     int64   `json:"accepted"`
 	Rejected     int64   `json:"rejected"`
+	RejectCount  int64   `json:"rejectcount"`
 	DSPS1        float64 `json:"dsps1"`
 	DSPS5        float64 `json:"dsps5"`
 	DSPS15       float64 `json:"dsps15"`