Add node peers, blue banners, glowing diff ranges, fix back navigation

- Show Bitcoin Core peer count on block height card (hover for in/out)
- BestSharePage disclaimers now use solid blue styling
- Difficulty distribution ranges glow from warm peach to deep red
- Back-to-dashboard buttons always navigate to dashboard instead of
  using browser history

api/internal/state/aggregator.go

@@ -98,6 +98,11 @@ type Snapshot struct {
 	HasLastZMQEvent   bool    `json:"has_last_zmq_event"`
 	TipChangedAge     float64 `json:"tip_changed_age"`              // seconds since tip height last changed
 
+	// Bitcoin Core peer connections.
+	PeerCount    int `json:"peer_count"`
+	PeersIn      int `json:"peers_in"`
+	PeersOut     int `json:"peers_out"`
+
 	// Share counters: raw counts (1 submission = 1 share regardless of diff).
 	// Session = since ckpool started; AllTime = persisted across restarts.
 	SessionAccepted int64 `json:"session_accepted"`
@@ -460,6 +465,13 @@ func (a *Aggregator) refresh(ctx context.Context) {
 		}
 	}
 
+	// --- bitcoind: peer connections ---
+	if ni, err := a.RPC.GetNetworkInfo(ctx); err == nil {
+		next.PeerCount = ni.Connections
+		next.PeersIn = ni.ConnectionsIn
+		next.PeersOut = ni.ConnectionsOut
+	}
+
 	// --- predicted difficulty adjustment ---
 	// Fetch the timestamp of the first block in the current retarget
 	// epoch (height - height%2016) once per epoch and cache it, then