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/fuzzing/json_fuzzer.cpp

@@ -0,0 +1,11 @@
+#include <ArduinoJson.h>
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  DynamicJsonDocument doc(4096);
+  DeserializationError error = deserializeJson(doc, data, size);
+  if (!error) {
+    std::string json;
+    serializeJson(doc, json);
+  }
+  return 0;
+}