Add last block earnings display to UI

Updated `updateUI()` in `main.js` to show last block earnings with a "+" prefix and "SATS" suffix. Modified `dashboard.html` to include a new span element that conditionally displays the earnings or defaults to "+0 SATS".

static/js/main.js

@@ -1693,6 +1693,13 @@ function updateUI() {
             data.btc_price != null ? "$" + numberWithCommas(parseFloat(data.btc_price).toFixed(2)) : "N/A"
         );
 
+        // Update last block earnings
+        if (data.last_block_earnings !== undefined) {
+            // Format with "+" prefix and "SATS" suffix
+            updateElementText("last_block_earnings",
+                "+" + numberWithCommas(data.last_block_earnings) + " SATS");
+        }
+
         // Network hashrate (already in EH/s but verify)
         // Improved version with ZH/s support:
         if (data.network_hashrate >= 1000) {

templates/dashboard.html

@@ -76,7 +76,7 @@
                         {{ metrics.last_block_time if metrics and metrics.last_block_time else "N/A" }}
                     </span>
                     —
-                    <span class="green">
+                    <span id="last_block_earnings" class="metric-value green">
                         {% if metrics and metrics.last_block_earnings %}
                         +{{ metrics.last_block_earnings|int|commafy }} SATS
                         {% else %}