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/Rtc_by_Makuna/library.json

@@ -0,0 +1,13 @@
+{
+    "name": "RTC",
+    "keywords": "RTC, DS1302, DS1307, DS3231, DS3234, AT24C32, clock",
+    "description": "A library that makes interfacing DS1302, DS1307, DS3231, and DS3234 Real Time Clock modules easy.",
+    "repository": {
+        "type": "git",
+        "url": "https://github.com/Makuna/Rtc.git"
+    },
+    "version": "2.3.5",
+    "frameworks": "arduino",
+    "platforms": "*"
+}
+