Conformance inc3: promote the corpus to a documented portable spec

Makes the host-neutral corpus a first-class language specification with
conformance levels, not just a regression suite.

- [suite label] is now a unique, stable case id (extract-corpus disambiguates
  duplicate labels with ' (N)' — one collision existed).
- certify.clj --profile emits test/conformance/profile.edn: every non-portable
  case classified by the host feature it requires (numerics/double-only,
  concurrency/snapshot, host/jvm-interop, host/arrays, host/janet,
  async/core-async, runtime/eval, reader/jolt, printer/jolt, strictness/jolt,
  impl/representation, bug). 2670 of 2919 cases are portable (pass on any faithful
  Clojure); 249 are feature-gated.
- SPEC.md documents the contract: row schema, the JVM oracle, conformance levels,
  the feature vocabulary, and a worked new-runtime harness — so hosting jolt
  elsewhere and proving it correct is read-one-file mechanical.

Janet gate 155 files 0 failed; certify + zero-janet gates green.

test/conformance/README.md

@@ -1,5 +1,10 @@
 # Conformance: certifying the corpus against reference Clojure
 
+> **See [SPEC.md](SPEC.md)** for the full host-neutral language-spec contract: the
+> corpus schema, conformance levels, the feature profile, and how to host jolt on a
+> new runtime. This README covers the certification tooling specifically.
+
+
 The corpus (`test/chez/corpus.edn`) is jolt's host-neutral behavioral suite — one
 row per case: `{:suite :label :expected :actual}`, where `:actual` is a Clojure
 source expression and `:expected` its result (or `:throws`). Runtime harnesses