Chez Phase 2 (inc P): clojure.string namespace (jolt-nfca)

Bring the clojure.string namespace up on Chez so aliased refs like s/split,
s/upper-case, s/join, s/replace resolve and run.

Three pieces. (1) The Chez AOT driver analyzes the whole user form before any
require runs, so a (require '[clojure.string :as s]) never registered the
alias in time; eval-e-with-prelude now recursively pre-evals require/use forms
against the ctx, which loads the aliased ns and registers the alias so the
analyzer resolves s/X to a clojure.string var. (2) emit-core-prelude emits
stdlib namespaces (clojure.string) as their own def-var! tier through the same
analyze->emit pipeline, so the runtime var-deref resolves. (3) natives-str.ss
def-var!s the str-* primitives clojure.string.clj is written over (upper/lower/
trim/triml/trimr/find/reverse-b/join/split/replace/replace-all), plus no-op
require/use. Regex split keeps interior empties and honors the limit (ported
the seed re-split); regex replace does $N backref expansion and fn replacement
(ported replacement-for). new RT/clj files added to the prelude fingerprint.

Corpus prelude floor 2026 -> 2078 (+52), 0 new divergences. _strns 28/28 vs
build/jolt. Four previously-CRASHING cases now emit+run and surface pre-existing
gaps (read-line vector eval-order x3, instance? clojure.lang.Atom) — allowlisted
with notes. full jpm test + conformance x3 green.

host/chez/jolt-chez.janet

@@ -21,7 +21,8 @@
            "host/chez/values.ss" "host/chez/collections.ss" "host/chez/seq.ss"
            "host/chez/atoms.ss" "host/chez/predicates.ss" "host/chez/regex.ss"
            "host/chez/ns.ss" "host/chez/post-prelude.ss" "host/chez/natives-meta.ss"
-           "host/chez/natives-str.ss" "host/chez/records.ss"]
+           "host/chez/natives-str.ss" "host/chez/records.ss"
+           "src/jolt/clojure/string.clj"]
     (array/push parts (slurp f)))
   (string/slice (string (hash (string/join parts))) 0))