add docker compose with persistent redis

.env.example

@@ -0,0 +1,17 @@
+# copy to .env and fill in, then: docker compose up -d
+
+# required: bcrypt hash. generate with:
+#   htpasswd -nbBC 10 "" 'your-password' | tr -d ':\n'
+HAUK_PASSWORD_HASH=
+
+# public url used in generated share links
+HAUK_PUBLIC_URL=http://localhost:8080/
+
+# max share lifetime in seconds (redis key TTL)
+HAUK_MAX_DURATION=86400
+
+# trust X-Forwarded-For; set true only when behind a reverse proxy
+HAUK_TRUST_PROXY=false
+
+# redis persistence: on => survives restart, off => in-memory only
+REDIS_PERSIST=on