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)

Caddyfile

@@ -1,7 +1,24 @@
 :8080 {
-    basic_auth /* {
-        # Set BASIC_AUTH_HASH on the server: caddy hash-password --plaintext 'YOUR_PWD'
-        admin {env.BASIC_AUTH_HASH}
+    handle /health {
+        respond 200
     }
-    reverse_proxy localhost:4213
+
+    handle /login {
+        reverse_proxy 127.0.0.1:8081
+    }
+
+    handle /query {
+        reverse_proxy 127.0.0.1:8081
+    }
+
+    handle {
+        forward_auth 127.0.0.1:8081 {
+            uri /auth
+            copy_headers Cookie
+        }
+        reverse_proxy localhost:7681 {
+            flush_interval -1
+        }
+    }
+
 }