Tree-shake: count #'x references; multi-app soundness smoke

Two things, both from studying Stalin's closed-world DCE:

1. Soundness fix: dce-collect-refs now counts a :the-var (#'x / (var x)) reference,
   not just a :var. Stalin's rule is that ANY reference — value position, not only a
   direct call — keeps the target live; a var referenced as #'x would otherwise be
   wrongly dropped. (My :var collection already covered value-position refs; this
   closes the the-var hole.)

2. host/chez/tree-shake-smoke.sh (make shakesmoke): builds example apps default vs
   --tree-shake and requires identical output — the real risk is shaking a binary
   that pulled libraries via deps.edn. Covers markdown/malli/commonmark/hiccup
   (git-lib apps). All produce byte-identical output shaken vs not, and drop
   ~0.8-1MB (malli 10.0MB -> 9.0MB) from the compiler-drop. Slow; not in the default
   gate. Skips without the examples repo.

Makefile

@@ -4,7 +4,7 @@
 # build step. `make test` is the full gate. `make remint` rebuilds the seed after a
 # source change.
 
-.PHONY: test ci values corpus unit smoke buildsmoke selfhost sci certify ffi transient infer directlink numeric inline remint
+.PHONY: test ci values corpus unit smoke buildsmoke selfhost sci certify ffi transient infer directlink numeric inline shakesmoke remint
 
 # Full gate (dev machine). Includes the self-host byte-fixpoint, which only holds
 # on the same Chez that minted the seed.
@@ -77,6 +77,12 @@ numeric:
 inline:
 	@chez --script test/chez/inline-test.ss
 
+# Tree-shake soundness: build example apps (incl. deps.edn git-lib apps) default vs
+# --tree-shake and require identical output. Slow (two builds per app); not in the
+# default gate. Skips without the examples repo / Chez kernel dev files.
+shakesmoke:
+	@sh host/chez/tree-shake-smoke.sh
+
 # JVM oracle: certify the corpus against reference Clojure. Skips if clojure absent.
 certify:
 	@if command -v clojure >/dev/null 2>&1; then \