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/conf_test/x86.cpp

@@ -0,0 +1,15 @@
+#include <ArduinoJson.h>
+
+static_assert(ARDUINOJSON_USE_LONG_LONG == 1, "ARDUINOJSON_USE_LONG_LONG");
+
+static_assert(ARDUINOJSON_SLOT_OFFSET_SIZE == 2,
+              "ARDUINOJSON_SLOT_OFFSET_SIZE");
+
+static_assert(ARDUINOJSON_LITTLE_ENDIAN == 1, "ARDUINOJSON_LITTLE_ENDIAN");
+
+static_assert(ARDUINOJSON_USE_DOUBLE == 1, "ARDUINOJSON_USE_DOUBLE");
+
+static_assert(sizeof(ARDUINOJSON_NAMESPACE::VariantSlot) == 16,
+              "sizeof(VariantSlot)");
+
+int main() {}