Scans #+begin_src lisp ... #+end_src blocks, strips strings and
comments, reports unbalanced parens per-block with line numbers.
Detects unterminated blocks (no matching #+end_src).
Zero dependencies (stdlib Python). Called from AGENTS.md step:
projects/check-parens/check-parens org/file.org
Move the development workflow details (TDD, REPL, literate programming,
branch policy) from top-level AGENTS.md into projects/AGENTS.md.
Top-level AGENTS.md now describes only the monorepo structure and
project list.
