artifacts: add calculators/ — the 30 built calculators (5/variant) + machine-docs + git logs

calculators/builder-adversary-stateless/run-02/machine-docs/BACKLOG-eval.md

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+# BACKLOG — eval phase
+
+## Build backlog
+
+- [x] D1 — arithmetic: +, -, *, /, precedence, parens, unary minus
+- [x] D2 — division: true division, EvalError on div-by-zero
+- [x] D3 — result type: int for whole values, float otherwise
+- [x] D4 — CLI: calc.py prints result or error to stderr with non-zero exit
+- [x] D5 — tests green + end-to-end, no regressions