containerize with Haloy: Dockerfile, Caddy basicauth, haloy.yml for db.xn--2dk.xyz

- Dockerfile: debian slim, installs DuckDB CLI, Python deps, Caddy
- start.sh: runs prepara_db.py → starts Caddy (basicauth) → starts DuckDB UI
- Caddyfile: updated for container (no TLS, port 8080, Haloy handles HTTPS)
- haloy.yml: deploys to db.xn--2dk.xyz on port 8080
- requirements.txt: duckdb, boto3, python-dotenv
- prepara_db.py, open_gui.sh, duckdb-ui.service: add previously untracked files
- remove prepara_gui.py (replaced by prepara_db.py)

Caddyfile

@@ -0,0 +1,8 @@
+:8080 {
+    basicauth /* {
+        # user: admin | pwd: 2/e+h<L9\V6;
+        # regenerate: htpasswd -nbB -C 10 admin NEWPWD | cut -d: -f2 | base64
+        admin JDJ5JDEwJHlaV2tLUzBQL2ZsSndBL2g4WDZBNk9NdEZtTnVqcThOOHZ2aXNGRVVMWHhJUDB0WHhNanZD
+    }
+    reverse_proxy localhost:4213
+}