Add explain.txt with plain EXPLAIN AST output for 00001_select_1#8

kyleconroy merged 2 commits intomainsqlc-dev/doubleclick:mainfrom

claude/fix-clickhouse-ast-json-01XiMdUgbBKTL1uEPAaajWJwsqlc-dev/doubleclick:claude/fix-clickhouse-ast-json-01XiMdUgbBKTL1uEPAaajWJwCopy head branch name to clipboard