Chez Phase 1 (increment 3i): regex via vendored irregex

Closes the last clojure.core prelude emit gap (parse-uuid): the whole
non-macro core now lowers to Scheme (prelude reach 355/355).

A #"..." literal analyzes to a :regex IR node. The Chez back end emits
a jolt-regex value over irregex (Alex Shinn, BSD), vendored as the
vendor/irregex submodule -- a portable Scheme regex with PCRE/Java-style
string patterns and first-class Chez support. host/chez/regex.ss wraps
jolt's re-* surface over it: irregex-match -> re-matches (anchored),
irregex-search -> re-find, groups as Clojure [whole g1 ...] vectors,
re-seq as a jolt seq. re-pattern/re-matches/re-find/re-seq/regex? are
def-var!'d into clojure.core so prelude / -e code resolves them.

They stay OUT of the subset native-ops on purpose: irregex's
Unicode/property-class semantics differ from the seed's byte-PEG
approximation, so keeping them prelude-only avoids dragging
engine-difference divergences into the subset-parity corpus. The Janet
back end punts :regex to the interpreter (the seed compiles #"..." to a
Janet PEG), so the main language is unchanged.

Only two adaptations for Chez's top level: a cond-expand shim (Chez's is
library-only) and a normalizing error wrapper (silences irregex's 1-arg
error warnings). rt.ss load is ~0.18s.

emit-test 131/131 (regex literal + re-* parity vs the CLI oracle);
prelude reach 355/355; Chez subset 672/672, 0 divergences; full gate
green.

jolt-core/jolt/analyzer.clj

@@ -21,6 +21,7 @@
                                form-vec? form-map? form-set? form-char?
                                form-literal? form-elements form-vec-items
                                form-map-pairs form-set-items form-special? compile-ns
+                               form-regex? form-regex-source
                                form-macro? form-expand-1 resolve-global
                                form-sym-meta host-intern! form-syntax-quote-lower
                                record-type? record-ctor-key form-position]]))
@@ -355,4 +356,8 @@
                                      (form-map-pairs form)))
      (form-set? form) (set-node (mapv #(analyze ctx % env) (form-set-items form)))
      (form-list? form) (analyze-list ctx form env)
+     ;; regex literal #"…" -> a :regex IR node (leaf). The Janet back end punts it
+     ;; (interpreter compiles via the seed PEG engine); the Chez back end emits a
+     ;; jolt-regex value over the vendored irregex.
+     (form-regex? form) {:op :regex :source (form-regex-source form)}
      :else (uncompilable "unsupported form"))))