feat: Wi-Fi provisioning via WiFiManager captive portal

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

WeatherPredictor/WeatherPredictor.ino

@@ -7,6 +7,7 @@
 #include "forecast.h"
 #include "history.h"
 #include "app_settings.h"
+#include "net.h"
 #include "state.h"
 
 AppState g_state;
@@ -51,6 +52,13 @@ void setup() {
   historyLoad();   // restore prior samples (empty on first ever boot)
   Serial.printf("history restored: %d samples\n", historyCount());
 
+  displaySplash("WiFi", "Connect / portal");
+  if (netBegin()) {
+    Serial.printf("WiFi connected: %s\n", netIP().c_str());
+  } else {
+    Serial.println(F("WiFi not connected - running offline"));
+  }
+
   // Seed first sample immediately.
   sampleNow();
   historyAdd(rtcEpoch(), g_state.mslHpa, g_state.tempC);