Chez Phase 1 (increment 3h): host-interop method-call emit

(.method target arg*) now analyzes to a :host-call IR node instead of
punting at analyze. The Chez back end lowers it to a jolt-host-call
dispatch for the methods the RT shims (.write -> port display,
.isDirectory -> file-directory?, .listFiles -> directory-list); any
other method stays out of subset (clean emit-time reject, so it can't
read as a compiled-but-broken corpus divergence). The Janet back end
punts ALL :host-call to the interpreter, same shape as letfn: compiles
on Chez, interprets on Janet, zero change to the main language.

Closes the io tier's print-method defmethods and file-seq: prelude emit
reach 348 -> 354/355 (50-io 20/20). The one remaining gap is the regex
literal in parse-uuid (needs a regex engine on Chez; deferred).

emit-test 122/122; Chez subset 672/672, 0 divergences; full gate green.

jolt-core/jolt/ir.clj

@@ -101,6 +101,8 @@
       (= op :fn)     (assoc node :arities (mapv (fn [a] (assoc a :body (f (get a :body))))
                                                 (get node :arities)))
       (= op :def)    (assoc node :init (f (get node :init)))
+      (= op :host-call) (assoc node :target (f (get node :target))
+                                    :args (mapv f (get node :args)))
       ;; :catch-body / :finally are optional; recurse them only when PRESENT.
       ;; Assoc'ing them nil-when-absent would turn the node into a phm (jolt's
       ;; nil-valued-key representation) and force backend densification — so we