Build container image in CI, bake in datasets, configure auth via env

- Dockerfile bakes the app and every CSV in data/ into an nginx image
- UI discovers data/*.csv via nginx JSON autoindex and offers a
  dropdown when there is more than one dataset
- docker-entrypoint.d/40-basic-auth.sh creates .htpasswd from
  BASIC_AUTH_USER / BASIC_AUTH_PASSWORD(_FILE) and refuses to start
  without credentials; replaces set-password.sh
- Gitea Actions workflow builds and pushes
  registry.traberph.de/public/interval_viz (latest, sha-*, semver)
- Escape resets the chart zoom

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

nginx/default.conf

@@ -9,7 +9,7 @@ server {
 
     gzip on;
     gzip_comp_level 6;
-    gzip_types text/css text/csv application/javascript;
+    gzip_types text/css text/csv application/javascript application/json;
 
     auth_basic "Heatpump";
     auth_basic_user_file /etc/nginx/.htpasswd;
@@ -19,9 +19,10 @@ server {
         include /etc/nginx/security-headers.conf;
     }
 
-    # the CSV is mounted separately so it can be replaced without touching the app
-    location = /history.csv {
-        alias /data/history.csv;
+    # data/ is listed as JSON so the UI can discover the CSV files
+    location /data/ {
+        autoindex on;
+        autoindex_format json;
         default_type text/csv;
         include /etc/nginx/security-headers.conf;
     }