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/_ioreader.janet

@@ -4,10 +4,10 @@
 # StringReader, and with-open's __close seam over both jhost readers and plain
 # :close maps. All Chez-native (host/chez/io.ss); no analyzer change. Reader/edn
 # runtime read (clojure.edn/read over a PushbackReader) stays jolt-r8ku.
-# Oracle = build/jolt.
+#
 #
 #   janet test/chez/_ioreader.janet
-(def jolt-bin (or (os/getenv "JOLT_BIN") "bin/jolt-chez"))
+(def jolt-bin (or (os/getenv "JOLT_BIN") "bin/joltc"))
 
 (defn io [body] (string "(do (require (quote [clojure.java.io :as io])) " body ")"))
 
@@ -47,11 +47,8 @@
 (var pass 0)
 (def fails @[])
 (each [expr expected] cases
-  (def [ocode oracle _] (run-capture "build/jolt" expr))
   (def [code got err] (run-capture jolt-bin expr))
   (cond
-    (not= ocode 0) (array/push fails [expr (string "ORACLE FAILED exit " ocode)])
-    (not= oracle expected) (array/push fails [expr (string "ORACLE MISMATCH want `" expected "` got `" oracle "`")])
     (not= code 0) (array/push fails [expr (string "exit " code "; err: " err)])
     (= got expected) (++ pass)
     (array/push fails [expr (string "want `" expected "`, got `" got "`")])))