Chez Phase 3 inc6b: runtime macros on the zero-Janet spine

The on-Chez analyzer (inc6a) skipped macros, so let/when/->/defn didn't
expand from source. Each core/stdlib defmacro now emits into the prelude as
(def-var! ns name <expander fn>) + (mark-macro! ns name); form-macro?/
form-expand-1 on Chez look up the macro flag (rt.ss var-macro-table) and
apply the expander to the unevaluated arg forms, and the analyzer re-analyzes
the result. The expander's syntax-quote template was lowered to construction
code at cross-compile time, so it builds the expansion via __sqcat/__sqvec/
__sqmap/__sqset/__sq1 (new host/chez/syntax-quote.ss) as Chez reader forms.

Emit the bare (fn ...), not (def NAME (fn ...)): analyzing a def would
host-intern! NAME as a non-macro stub in the build ctx, and that stub makes a
later (require '[stdlib-ns]) skip loading the real macro — with-pprint-dispatch
then resolved as a fn and returned its unexpanded template. Wrapping the
lambda in def-var! manually never interns NAME. Fuller build-ctx isolation
(so stdlib cases pass instead of crash) tracked in jolt-lpvi.

__sqset builds a real set VALUE, not the reader's tagged-set form — a runtime
`#{~@xs} must be a set, not a map. form-set? additionally recognizes a pset so
a macro template's #{...} expansion still re-analyzes as a set literal.

spine-test 35/35 (20 macro cases: when/when-not/let/->/->>/and/or/cond/if-not/
defn run zero-Janet from source). Prelude parity 2280->2295, 0 new divergences.
Full Janet gate green.

host/chez/jolt-chez.janet

@@ -25,6 +25,7 @@
            "host/chez/natives-str.ss" "host/chez/records.ss"
            "host/chez/host-class.ss" "host/chez/io.ss"
            "host/chez/inst-time.ss" "host/chez/reader.ss" "host/chez/math.ss"
+           "host/chez/syntax-quote.ss"
            "host/chez/host-static.ss" "host/chez/dot-forms.ss"
            "src/jolt/clojure/string.clj" "src/jolt/clojure/walk.clj"
            "src/jolt/clojure/template.clj" "src/jolt/clojure/edn.clj"