Fix flash dialog stacking and key exchange reliability

1. Dismiss waiting dialog when flash progress dialog starts,
   preventing orphaned spinner dialog after flash completes.
2. Increase key exchange retries from 3 to 5 and initial delay
   from 500ms to 1000ms to give ESP more time to be ready
   after USB permission grant.

android/app/src/main/java/com/eddy/atomrelay/SettingsActivity.kt

@@ -204,6 +204,8 @@ class SettingsActivity : AppCompatActivity() {
     }
 
     private fun doFlashing(usbManager: UsbManager, device: UsbDevice) {
+        dialog?.dismiss()
+        dialog = null
         showProgressDialog("Firmware Flashen", "Initialiseren...", STYLE_HORIZONTAL)
 
         flasher = EspFlasher(this)
@@ -338,8 +340,8 @@ class SettingsActivity : AppCompatActivity() {
         try {
             setupCdcControl(connection, device)
 
-            for (attempt in 1..3) {
-                Thread.sleep(500)
+            for (attempt in 1..5) {
+                Thread.sleep(1000L)
 
                 flushReadBuffer(connection, epIn)
 
@@ -392,7 +394,7 @@ class SettingsActivity : AppCompatActivity() {
                 Log.w(TAG, "Attempt $attempt: no KEY response, retrying")
             }
 
-            return KeyResult.Error("Geen sleutel gevonden na 3 pogingen")
+            return KeyResult.Error("Geen sleutel gevonden na 5 pogingen")
         } catch (e: Exception) {
             Log.e(TAG, "Key exchange error", e)
             return KeyResult.Error("Fout: ${e.message}")