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>

.gitignore

@@ -0,0 +1,5 @@
+# secrets
+nginx/.htpasswd
+# personal data export
+history.csv
+.env