feat: refine portal flow and examples

examples/CustomPortalContent/CustomPortalContent.ino

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+#include <Arduino.h>
+#include <WiFiManager.h>
+
+WiFiManager portal;
+WiFiManagerParameter brokerHost("broker_host", "MQTT broker", "mqtt.local", 40);
+
+void setup() {
+    Serial.begin(115200);
+
+    portal.portalAddParameter(&brokerHost);
+    portal.portalAddInfoSection({
+        "device", "Example device",
+        {{"firmware", "Firmware", "1.0.0"}, {"sensor", "Sensor", "Ready"}},
+    });
+    portal.portalAddHomeCard({
+        "hint", "What this example adds", PortalHomeCardKind::Callout,
+        "A normal text setting, a status section, and a home-page callout.", {},
+    });
+
+    portal.setSaveParamsCallback([](WiFiManager::WiFiManagerRequestArgs) {
+        Serial.print("MQTT broker selected: ");
+        Serial.println(brokerHost.getValue());
+    });
+    portal.setConfigPortalTimeout(180);
+
+    portal.autoConnect("WiFiManager Content", "example-pass");
+}
+
+void loop() { portal.process(); }

examples/CustomPortalContent/README.md

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+# Custom Portal Content
+
+This example keeps WiFiManager’s portal navigation, validation, and captive behaviour, while adding three application-owned pieces of content:
+
+- an editable MQTT broker host field;
+- a compact device-information section;
+- a callout on the portal overview.
+
+It opens **WiFiManager Content** with password **example-pass** until it has working station credentials. Save the form, then inspect serial output to see the selected broker value.
+
+The parameter object is global because WiFiManager reads it for the lifetime of the portal. In a real application, copy the value into that application’s own validated persistent configuration inside the save callback.
+
+See [Portal UI](../../docs/PORTAL_UI.md) and the shared [example guide](../README.md).

examples/CustomPortalContent/platformio.ini

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+[platformio]
+default_envs = esp8266
+src_dir = .
+
+[common]
+framework = arduino
+lib_ldf_mode = deep+
+lib_deps =
+    WiFiManager=symlink://../..
+
+[env:esp8266]
+extends = common
+platform = espressif8266
+board = d1_mini
+platform_packages =
+    platformio/framework-arduinoespressif8266 @ https://github.com/esp8266/Arduino.git#521ae60a89e64bb0d1eb7a0b7addf620ced5cad3
+
+[env:esp32]
+extends = common
+platform = https://github.com/pioarduino/platform-espressif32/releases/download/51.03.05/platform-espressif32.zip
+board = esp32dev
+build_unflags = -std=gnu++11
+build_flags =
+    -std=gnu++14
+    -DSOC_WIFI_SUPPORTED=1
+    -I${platformio.packages_dir}/framework-arduinoespressif32/libraries/Network/src