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

ui/src/lib/PoolOverview.svelte

@@ -208,7 +208,12 @@
   <div class="card height-card" class:new-block={heightFlash}>
     <div class="stat-label">Block height</div>
     <div class="stat-value">{height ? height.toLocaleString() : "—"}</div>
-    <div class="stat-sub">{data.chain?.chain === "main" ? "mainnet" : data.chain?.chain ?? "—"}</div>
+    <div class="stat-sub">
+      {data.chain?.chain === "main" ? "mainnet" : data.chain?.chain ?? "—"}
+      {#if data.peer_count > 0}
+        <span class="peers" title="{data.peers_in} inbound · {data.peers_out} outbound">&nbsp;· {data.peer_count} peers</span>
+      {/if}
+    </div>
   </div>
 
   <div class="card">