Delete the Janet host — Chez is the sole substrate

Remove the Janet seed (src/jolt/*.janet: reader, value layer, vars/ns, the
tree-walking interpreter, the Janet backend, the optimizing compiler), the
Janet->Scheme cross-compiler (host/chez/{driver,emit,jolt-chez}.janet),
bin/jolt-chez, the jpm build (project.janet) and the Janet test runner
(run-tests.janet), plus the entire Janet test suite. jolt now builds and runs
on Chez alone: bin/joltc off the checked-in seed, bootstrap.ss to rebuild it.

The portable Clojure stays: jolt-core/**, host/chez/**.ss, and the stdlib +
tooling under src/jolt/clojure + src/jolt/jolt (read by the seed build, no
Janet). The gate is 'make test' (self-host, corpus, unit, cli smoke, certify).
Drop the sci and clojure-test-suite submodules (used only by deleted Janet
integration tests); irregex stays.

Filesystem corpus/unit cases that probed project.janet now probe README.md.

jolt-cf1q.6

Makefile

@@ -4,16 +4,20 @@
 # build step. `make test` is the full gate. `make remint` rebuilds the seed after a
 # source change.
 
-.PHONY: test corpus unit smoke selfhost certify remint
+.PHONY: test values corpus unit smoke selfhost certify remint
 
 # Full gate. Each step exits non-zero on failure, failing the target.
-test: selfhost corpus unit smoke certify
+test: selfhost values corpus unit smoke certify
 	@echo "OK: all gates passed"
 
 # Self-host fixpoint: bootstrap.ss rebuild == checked-in seed.
 selfhost:
 	@sh host/chez/selfcheck.sh
 
+# Value-model unit tests (nil/truthiness/collections on Chez).
+values:
+	@chez --script test/chez/values-test.ss
+
 # Corpus conformance vs JVM-sourced expecteds (allowlist + floor).
 corpus:
 	@chez --script host/chez/run-corpus.ss