Implement BLE OTA

web/index.html

@@ -192,6 +192,29 @@
       </button>
     </div>
 
+    <div class="section-label" style="margin-top:8px">Firmware Update (OTA)</div>
+    <div class="card ota-card" id="otaCard">
+      <div class="ota-notice">
+        <div class="ota-notice-icon">⚠</div>
+        <div>
+          <div class="ota-notice-title">Browser OTA not available</div>
+          <div class="ota-notice-body">Chrome blocks the Nordic Legacy DFU service UUID used by this bootloader. Use <strong>nRF Connect</strong> (mobile or desktop) to upload firmware instead.</div>
+        </div>
+      </div>
+      <ol class="ota-steps">
+        <li>Build firmware: <code>pio run</code> → produces <code>firmware_dfu.zip</code></li>
+        <li>Click <strong>Enter DFU Mode</strong> below — device reboots as <em>XIAO_DFU</em></li>
+        <li>Open nRF Connect → connect to <em>XIAO_DFU</em> → DFU → select <code>firmware_dfu.zip</code></li>
+      </ol>
+      <div class="ota-btn-row" style="grid-template-columns:1fr">
+        <button class="cmd-btn ota-trigger" id="btnOTA" onclick="sendOTATrigger()" disabled>
+          <span class="cmd-icon">⟳</span><span>Enter DFU Mode</span>
+          <span class="cmd-desc">Reboots device into XIAO_DFU so nRF Connect can upload firmware.</span>
+        </button>
+      </div>
+      <div class="ota-status-row"><div class="ota-status" id="otaStatus"></div></div>
+    </div>
+
     <div class="section-label" style="margin-top:8px">Event Log</div>
     <div class="console" id="console"></div>
 
@@ -249,6 +272,7 @@
   </div>
 </main>
 
+
 <div class="overlay" id="overlay">
   <div class="modal">
     <h3>⚠ Factory Reset</h3>