Pure-Chez test gates (no Janet)

Add a Janet-free gate so correctness can be judged with only Chez + Clojure:
- host/chez/run-corpus.ss: corpus.edn vs JVM expecteds, lifting the per-case ns
  isolation from the old Janet driver; reads corpus.edn via the jolt reader.
- host/chez/run-unit.ss + test/chez/unit.edn: the host-specific unit cases,
  evaluated in-process and compared to baked expecteds.
- host/chez/selfcheck.sh: self-host fixpoint (bootstrap.ss rebuild == checked-in seed).
- host/chez/smoke.sh: real bin/joltc CLI smoke.
- host/chez/remint.sh: re-mint the seed to a byte-fixpoint after a source change.
- Makefile: 'make test' runs the lot; 'make remint' rebuilds the seed.

Numbers match the Janet gate: corpus 2679/2757 0 new div, unit 450/450, certify
0 new/0 stale.

jolt-cf1q.6

host/chez/selfcheck.sh

@@ -0,0 +1,18 @@
+#!/bin/sh
+# self-host fixpoint gate: bootstrap.ss rebuilds the prelude + compiler image from
+# source on pure Chez; the rebuild must equal the checked-in seed byte-for-byte. If
+# it doesn't, a seed source changed without a re-mint — run `make remint`.
+set -e
+root="$(CDPATH= cd -- "$(dirname -- "$0")/../.." && pwd)"
+cd "$root"
+tmp="$(mktemp -d)"
+trap 'rm -rf "$tmp"' EXIT
+chez --script host/chez/bootstrap.ss \
+  host/chez/seed/prelude.ss host/chez/seed/image.ss "$tmp/p.ss" "$tmp/i.ss" >/dev/null
+if diff -q host/chez/seed/prelude.ss "$tmp/p.ss" >/dev/null \
+   && diff -q host/chez/seed/image.ss "$tmp/i.ss" >/dev/null; then
+  echo "self-host fixpoint: rebuild == checked-in seed"
+else
+  echo "self-host FAILED: bootstrap rebuild != checked-in seed; run 'make remint'" >&2
+  exit 1
+fi