Import ESP_UniClock (upstream 1189810)

Vendored from https://github.com/gpeter62/ESP_UniClock: the sketch
source, the web UI and the libraries the ESP8266 build needs, unpacked
from the bundled zips. Adds a PlatformIO project for the ESP-12. The
source is unchanged; local changes follow as separate commits.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

firmware/uniclock/lib/arduino-home-assistant-main/examples/availability/README.md

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+# Home Assistant availability example
+
+This example shows how to use "availability" feature of the Home Assistant.
+It's supported only by following device types:
+* Binary sensor
+* Sensor
+* Switch
+* HVACs
+* Fans
+
+## Initialization and usage
+
+Availability feature is turned off by default. In order to turn it on for the specific
+sensor/switch you need to set initial state of the unit by calling `setAvailability` method.
+
+Example:
+```cpp
+...
+HABinarySensor sensor("input", "door", true, mqtt);
+
+void setup() {
+    // ...
+
+    // method must be called before `mqtt.begin(...)`
+    sensor.setAvailability(false); // offline
+
+    mqtt.begin(BROKER_ADDR);
+}
+...
+```
+
+After availability is set for the very first time you can call `setAvailability` in any time.
+Each time the method is called, the device will publish MQTT message to the broker.

firmware/uniclock/lib/arduino-home-assistant-main/examples/availability/availability.ino

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+#include <Ethernet.h>
+#include <ArduinoHA.h>
+
+#define INPUT_PIN       9
+#define BROKER_ADDR     IPAddress(192,168,0,17)
+
+byte mac[] = {0x00, 0x10, 0xFA, 0x6E, 0x38, 0x4A};
+unsigned long lastReadAt = millis();
+unsigned long lastAvailabilityToggleAt = millis();
+bool lastInputState = false;
+
+EthernetClient client;
+HADevice device(mac, sizeof(mac));
+HAMqtt mqtt(client, device);
+
+// "input" is unique ID of the sensor. You should define you own ID.
+// "door" is device class (based on the class HA displays different icons in the panel)
+// "true" is initial state of the sensor. In this example it's "true" as we use pullup resistor
+HABinarySensor sensor("input", "door", true);
+
+void setup() {
+    pinMode(INPUT_PIN, INPUT_PULLUP);
+    lastInputState = digitalRead(INPUT_PIN);
+
+    // you don't need to verify return status
+    Ethernet.begin(mac);
+
+    // turn on "availability" feature
+    // this method also sets initial availability so you can use "true" or "false"
+    sensor.setAvailability(false);
+
+    lastReadAt = millis();
+    lastAvailabilityToggleAt = millis();
+
+    // set device's details (optional)
+    device.setName("Arduino");
+    device.setSoftwareVersion("1.0.0");
+
+    sensor.setName("Door sensor"); // optional
+
+    mqtt.begin(BROKER_ADDR);
+}
+
+void loop() {
+    Ethernet.maintain();
+    mqtt.loop();
+
+    if ((millis() - lastReadAt) > 30) { // read in 30ms interval
+        // library produces MQTT message if a new state is different than the previous one
+        sensor.setState(digitalRead(INPUT_PIN));
+        lastInputState = sensor.getState();
+        lastReadAt = millis();
+    }
+
+    if ((millis() - lastAvailabilityToggleAt) > 5000) {
+        sensor.setAvailability(!sensor.isOnline());
+        lastAvailabilityToggleAt = millis();
+    }
+}