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/README.md

@@ -0,0 +1,22 @@
+# Rtc
+
+Arduino Real Time Clock library.  
+An RTC library with deep device support.
+
+[![Donate](https://img.shields.io/badge/paypal-donate-yellow.svg)](https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=6AA97KE54UJR4)
+
+For quick questions jump on Gitter and ask away.  
+[![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/Makuna/Rtc?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
+
+For bugs, make sure there isn't an active issue and then create one.
+
+## Documentation
+[See Wiki](https://github.com/Makuna/Rtc/wiki)
+
+## Installing This Library (prefered, you just want to use it)
+Open the Library Manager and search for "Rtc by Makuna" and install
+
+## Installing This Library From GitHub (advanced, you want to contribute)
+Create a directory in your Arduino\Library folder named "Rtc"
+Clone (Git) this project into that folder.  
+It should now show up in the import list when you restart Arduino IDE.