schema: use BD GraphQL API for enrichment, add file tree and schema artifacts

- Replace S3 bigquery_tables metadata lookup with paginated GraphQL API call
  to fetch table and column descriptions from Base dos Dados
- Add gera_schemas.py for schema compilation and S3 inventory
- Add schemas.json and file_tree.md as generated reference artifacts
- Add websocket proxy in Caddyfile for ttyd on port 7681
- Ignore generated context/ artifacts in .gitignore
- Add openai to requirements.txt

requirements.txt

@@ -1,3 +1,4 @@
 duckdb
 boto3
 python-dotenv
+openai