Fix WiFi file transfer crash by adding initialization delay

Fixed a critical bug where WiFi file transfer would crash and lock the device
when accessed directly. The issue was caused by missing initialization time
after WiFi.mode(WIFI_STA) call.

Root cause:
- Hotspot mode includes delay(100) after WiFi.mode(WIFI_AP) to allow hardware initialization
- Join Network mode was missing this delay after WiFi.mode(WIFI_STA)
- Without the delay, ESP32 WiFi hardware wasn't properly initialized
- This caused crashes when starting the web server in STA mode

Fix:
- Added delay(100) after WiFi.mode(WIFI_STA) in onNetworkModeSelected()
- Matches the proven initialization pattern used in hotspot mode
- Comment added to explain the purpose of the delay

This explains why going to hotspot first and exiting worked - hotspot mode
properly initialized the WiFi hardware, which remained stable for subsequent
file transfer operations.

src/activities/network/CrossPointWebServerActivity.cpp

@@ -138,6 +138,7 @@ void CrossPointWebServerActivity::onNetworkModeSelected(const NetworkMode mode)
     // STA mode - launch WiFi selection
     Serial.printf("[%lu] [WEBACT] Turning on WiFi (STA mode)...\n", millis());
     WiFi.mode(WIFI_STA);
+    delay(100);  // Allow WiFi hardware to initialize before proceeding
 
     state = WebServerActivityState::WIFI_SELECTION;
     Serial.printf("[%lu] [WEBACT] Launching WifiSelectionActivity...\n", millis());