fix: BLE connection leak on page unload and retry timer cleanup

- onUnload disconnects BLE if not in 'done' state (prevents connection leak)
- onUnload clears retry timer to prevent setData on dead page
- Store retry setTimeout ref for proper cleanup

miniprogram/pages/ble-connect/ble-connect.js

@@ -34,8 +34,15 @@ Page({
 
   onUnload: function () {
     clearTimeout(this._scanTimer)
+    clearTimeout(this._retryTimer)
     ble.stopScan()
-    if (this._onBindResult) ble.off('bind_result', this._onBindResult)
+    if (this._onBindResult) {
+      ble.off('bind_result', this._onBindResult)
+      this._onBindResult = null
+    }
+    if (this.data.state !== 'done') {
+      ble.disconnect()
+    }
   },
 
   startBleConnect: function () {
@@ -98,7 +105,7 @@ Page({
       self._onBindResult = null
     }
     ble.disconnect()
-    setTimeout(function () {
+    self._retryTimer = setTimeout(function () {
       self.startBleConnect()
     }, 1000)
   },