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>

nginx/security-headers.conf

@@ -0,0 +1,7 @@
+# Included per location: a location's own add_header drops inherited ones.
+add_header X-Content-Type-Options "nosniff" always;
+add_header X-Frame-Options "DENY" always;
+add_header Referrer-Policy "no-referrer" always;
+# Plotly injects inline styles and exports PNGs via data:/blob: URLs
+add_header Content-Security-Policy "default-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data: blob:; object-src 'none'; base-uri 'none'; frame-ancestors 'none'" always;
+add_header Cache-Control "no-cache" always;