replace duckdb-ui with ttyd shell: add /query HTTP endpoint, fix utf-8/locale, region config

- swap DuckDB UI for ttyd web terminal (--writable, -readonly db)
- add POST /query endpoint with X-Password auth for curl-based SQL execution
- fix UTF-8 rendering: set LANG/LC_ALL=C.UTF-8 in container
- pass BUCKET_REGION env var for correct S3 signing region
- simplify start.sh: drop Xvfb, views.duckdb generation, blocking duckdb -ui
- add less, ncurses-bin to Dockerfile for proper pager/terminal support
- update Caddyfile: single route to ttyd with flush_interval -1 for websocket
- update README to reflect current architecture and document /query usage
- remove duckdb-ui.service, schemas.json, file_tree.md (generated artifacts)

.env.sample

@@ -12,3 +12,6 @@ S3_CONCURRENCY=""
 PARALLEL_UPLOADS=""
 AWS_ACCESS_KEY_ID=""
 AWS_SECRET_ACCESS_KEY=""
+
+# Caddy serving duckdb
+BASIC_AUTH_PASSWORD=""