jolt build: --opt mode turns on the inference passes (Phase 4 stage 4a)

Wire the optimization gate to build mode. inline-enabled? (which gates the
inference + flatten-lets + scalar-replace passes in jolt.passes/run-passes) was
hardwired off, so those passes had never run on Chez at all. host-contract now
exposes a settable hc-optimize? flag; `jolt build --opt` flips it on during app
emission.

Kept off for the default release build for now: the passes are sound by design
(RFC 0005/0006) but unexercised on Chez, so release stays on the proven
var-deref codegen until they're validated against the corpus. --opt is the
opt-in fast path. buildsmoke checks both modes produce the same result.

This does not yet deliver direct call binding — the backend has no direct-link
emission path (every :var call still routes through jolt-invoke/var-deref) and
the inline-ir host stash is still a stub. Those are the remaining stage-4 levers.

host/chez/build-smoke.sh

@@ -22,11 +22,22 @@ want='HELLO FROM A BUILT BINARY!
 HELLO FROM A BUILT BINARY!
 args: [alpha bb ccc]
 sum: 10'
-if [ "$got" = "$want" ]; then
-  echo "build smoke: passed"
-else
+if [ "$got" != "$want" ]; then
   echo "  FAIL: binary output mismatch"
   echo "--- want ---"; echo "$want"
   echo "--- got ----"; echo "$got"
   exit 1
 fi
+
+# Optimized mode (inference + flatten + scalar-replace) must produce the same
+# result — a sanity check that the passes don't miscompile this app.
+if ! JOLT_PWD="$app" bin/joltc build -m app.core -o "$out" --opt >/dev/null 2>&1; then
+  echo "  FAIL: jolt build --opt exited non-zero"; exit 1
+fi
+got_opt="$(cd / && "$out" alpha bb ccc 2>&1)"
+if [ "$got_opt" != "$want" ]; then
+  echo "  FAIL: --opt binary output mismatch"
+  echo "--- got ----"; echo "$got_opt"
+  exit 1
+fi
+echo "build smoke: passed (release + optimized)"