docs: move setup to README, tighten CLAUDE.md

[masterleopold]

CLAUDE.md carried the public-facing setup steps while README.md had none — a reader cloning the repo had no way to build the rfl binding, which the whole suite depends on.

README.md gains ## Setup and ## Running: the sibling-checkout requirement, why rfl is deliberately not a pyproject.toml dependency, and the fact that harness/validate.py imports rfl at module scope (so the suite will not even collect until maturin develop succeeds). Also notes that few-shot reads the sibling rfl checkout at runtime while spec-only does not — only spec-only works from a standalone clone.

CLAUDE.md keeps only what matters while editing, and gains four things that previously required reading several files to discover:

• the run.py data flow — retarget runs against the first schema-passing sample, and results/ is overwritten while the README table is hand-maintained;
• the hermetic-CI rule (no network in tests; mock the Anthropic client as tests/test_claude.py does);
• the three places a new task must be registered (tasks/, reference_skills/, _ROUTES in planner/mock.py) plus the GROUP_A/GROUP_B split in tests/test_suite.py;
• the retarget_outcome precedence rule from 9681183 — the beyond_engine check must run before the capability_absent match, since rfl reports unimplemented primitives as capability_absent too.

Docs only; no code touched. pytest -q → 35 passed. python run.py --planner mock regenerates results/mock-spec-only.md byte-identical, confirming the published mock table still matches the post-9681183 classifier.

🤖 Generated with Claude Code

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