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/JsonArray/std_string.cpp

@@ -0,0 +1,31 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+static void eraseString(std::string &str) {
+  char *p = const_cast<char *>(str.c_str());
+  while (*p) *p++ = '*';
+}
+
+TEST_CASE("std::string") {
+  DynamicJsonDocument doc(4096);
+  JsonArray array = doc.to<JsonArray>();
+
+  SECTION("add()") {
+    std::string value("hello");
+    array.add(value);
+    eraseString(value);
+    REQUIRE(std::string("hello") == array[0]);
+  }
+
+  SECTION("operator[]") {
+    std::string value("world");
+    array.add("hello");
+    array[0] = value;
+    eraseString(value);
+    REQUIRE(std::string("world") == array[0]);
+  }
+}