[claude] Re-implement Bitcoin block height counter (#480) (#495)

app.js

@@ -1695,4 +1695,36 @@ function triggerHarnessPulse() {
   }
 }
 
+// === BITCOIN BLOCK HEIGHT ===
+(function initBitcoin() {
+  const blockHeightDisplay = document.getElementById('block-height-display');
+  const blockHeightValue = document.getElementById('block-height-value');
+  if (!blockHeightDisplay || !blockHeightValue) return;
+
+  let lastKnownBlockHeight = null;
+
+  async function fetchBlockHeight() {
+    try {
+      const res = await fetch('https://blockstream.info/api/blocks/tip/height');
+      if (!res.ok) return;
+      const height = parseInt(await res.text(), 10);
+      if (isNaN(height)) return;
+
+      if (lastKnownBlockHeight !== null && height !== lastKnownBlockHeight) {
+        blockHeightDisplay.classList.remove('fresh');
+        void blockHeightDisplay.offsetWidth;
+        blockHeightDisplay.classList.add('fresh');
+      }
+
+      lastKnownBlockHeight = height;
+      blockHeightValue.textContent = height.toLocaleString();
+    } catch (_) {
+      // Network unavailable
+    }
+  }
+
+  fetchBlockHeight();
+  setInterval(fetchBlockHeight, 60000);
+})();
+
 init();