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/ArduinoJson/extras/tests/JsonObject/invalid.cpp

@@ -0,0 +1,35 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+using namespace Catch::Matchers;
+
+TEST_CASE("JsonObject::invalid()") {
+  JsonObject obj;
+
+  SECTION("SubscriptFails") {
+    REQUIRE(obj["key"].isNull());
+  }
+
+  SECTION("AddFails") {
+    obj["hello"] = "world";
+    REQUIRE(0 == obj.size());
+  }
+
+  SECTION("CreateNestedArrayFails") {
+    REQUIRE(obj.createNestedArray("hello").isNull());
+  }
+
+  SECTION("CreateNestedObjectFails") {
+    REQUIRE(obj.createNestedObject("world").isNull());
+  }
+
+  SECTION("serialize to 'null'") {
+    char buffer[32];
+    serializeJson(obj, buffer, sizeof(buffer));
+    REQUIRE_THAT(buffer, Equals("null"));
+  }
+}