docs: add CLAUDE.md with engineering standards, SQL style, review policy

Author: NikolayS

CLAUDE.md

@@ -0,0 +1,26 @@
+# CLAUDE.md
+
+## Engineering Standards
+
+Follow the rules at https://gitlab.com/postgres-ai/rules/-/tree/main/rules — always pull latest before starting work.
+
+## SQL Style
+
+- Lowercase keywords (`select`, `from`, `where` — not `SELECT`, `FROM`, `WHERE`)
+- `<>` not `!=`
+
+## CI
+
+GitHub Actions (`test.yml`): runs on push and PRs — tests across PostgreSQL 13, 14, 15, 16, 17, 18.
+
+## Code Review
+
+All changes go through PRs. Before merging, run a REV review (https://gitlab.com/postgres-ai/rev/) and post the report as a PR comment. REV is designed for GitLab but works on GitHub PRs too.
+
+Never merge without explicit approval from the project owner.
+
+## Stack
+
+- Pure SQL reports loaded via `psql` (`\i start.psql`)
+- Interactive menu system — user picks a report number
+- Works on any Postgres 13+ including managed services (RDS, Cloud SQL, AlloyDB, etc.)