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/scripts/get-release-page.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+set -eu
+
+VERSION="$1"
+CHANGELOG="$2"
+FRONTMATTER="$3"
+
+cat << END
+---
+branch: v6
+version: $VERSION
+date: '$(date +'%Y-%m-%d')'
+$(cat "$FRONTMATTER")
+---
+
+$(awk '/\* /{ FOUND=1; print; next } { if (FOUND) exit}' "$CHANGELOG")
+END