Add heatpump compressor cycle analysis web app

Static page that plots Home Assistant on/off history of the heatpump
compressor with pan/zoom, per-phase hover durations and statistics
(min/max/mean/median, total on-time, duty cycle) for the visible range.
English/German UI. Served by nginx in Docker with basic auth, CSP and
a healthcheck; Plotly is vendored locally.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

set-password.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+# Creates nginx/.htpasswd for HTTP basic auth.
+# Usage: ./set-password.sh <user> [password]    (prompts for the password if omitted)
+set -eu
+
+user="${1:?usage: $0 <user> [password]}"
+case "$user" in *:*) echo "user name must not contain ':'" >&2; exit 1 ;; esac
+
+if [ $# -ge 2 ]; then
+    hash=$(openssl passwd -apr1 "$2")
+else
+    hash=$(openssl passwd -apr1)
+fi
+
+file="$(dirname "$0")/nginx/.htpasswd"
+[ -d "$file" ] && rmdir "$file"   # docker creates a directory if the file was missing on first start
+umask 077
+printf '%s:%s\n' "$user" "$hash" > "$file"
+chmod 644 "$file"                 # nginx workers must be able to read it
+echo "Wrote $file for user '$user'. Run 'docker compose restart' if the container is already running."