Move the Chez test oracle off Janet

The unit tests in test/chez/_*.janet now drive bin/joltc (the zero-Janet
spine) and judge against baked expected values instead of a live build/jolt
run. Ten of them captured the oracle from build/jolt per case; their values
are now literals (one env-dependent javastatic case became a predicate so it
stays portable). The rest already had literal expecteds with a redundant
build/jolt sanity check, now dropped.

Retire emit-test/emit-parity/reader-parity: they compared the Chez/Clojure
path against a live Janet evaluation, emitter, or reader. That migration check
is done, and run-corpus-zero-janet (Chez analyzer vs the JVM corpus) plus
certify.clj cover correctness now.

Rewrite the README for the current zero-Janet gate.

jolt-5oci

test/chez/_var_meta.janet

@@ -1,16 +1,16 @@
 # jolt-zikh — var def-time metadata capture (^:private / ^Type tag / docstring).
 # (meta (var v)) must carry the def-time reader metadata + :ns/:name, matching the
-# JVM-canonical build/jolt. TDD harness: bin/jolt-chez -e per case, last line ==
+# JVM-canonical reference. TDD harness: bin/joltc -e per case, last line ==
 # expected.
 #
 #   janet test/chez/_var_meta.janet
-(def jolt-bin (or (os/getenv "JOLT_BIN") "bin/jolt-chez"))
+(def jolt-bin (or (os/getenv "JOLT_BIN") "bin/joltc"))
 
 (def cases
   # NOTE: ^{:map} metadata on a def name (e.g. (def ^{:doc "hi"} dv 1)) reads as
   # (def (with-meta name m) v) and is uncompilable for the COMPILER generally
-  # (analyzer.clj rejects it; the Janet back end punts to its interpreter, which
-  # Chez lacks) — out of subset, not a meta-capture gap. Shorthand ^:kw / ^Type
+  # (analyzer.clj rejects it) — out of subset, not a meta-capture gap. Shorthand
+  # ^:kw / ^Type
   # and the docstring form keep the name a plain symbol, so they're in scope.
   [["^:private on var"   "(do (def ^:private pv 1) (:private (meta (var pv))))"      "true"]
    ["^Type tag on var"   "(do (def ^String tv \"a\") (:tag (meta (var tv))))"        "String"]