core: variadic bit ops, set? covers sorted sets, if rejects extra forms

Three canonical-conformance fixes from the post-shrink batch:

- bit-and/bit-or/bit-xor/bit-and-not get Clojure's variadic arities as
  20-coll shells folding the binary host ops (now __bit-* seams). 2-arg call
  sites still compile to the native janet op via the backend's native-ops
  table. The passes.clj constant-fold table now names the seams — the public
  fns are overlay and don't exist when the compiler loads (this briefly broke
  every compile-mode init).

- core-set? recognizes the :jolt/sorted-set representation (jolt-dpn):
  (set? (sorted-set 1)) was false, and ifn? on sorted sets inherited the bug.

- (if) / (if test) / (if test then else extra) throw in both the analyzer
  and the interpreter — spec 03-special-forms X1, now marked verified.

Suite 4704 -> 4706; bench and the greeter example benchmark are flat.

jolt-core/clojure/core/20-coll.clj

@@ -17,6 +17,25 @@
 ;; even?/odd? stay in the seed: (filter even? ...) is idiomatic-hot and the
 ;; overlay versions cost an extra call layer per element (seq-pipe bench 4x).
 
+;; Variadic bit ops — canonical Clojure arities folding the binary host op
+;; (__bit-* seams). 2-arg call sites still compile to the native janet op via
+;; the backend's native-ops table, so the binary fast path is unchanged.
+(defn bit-and
+  ([x y] (__bit-and x y))
+  ([x y & more] (reduce __bit-and (__bit-and x y) more)))
+
+(defn bit-or
+  ([x y] (__bit-or x y))
+  ([x y & more] (reduce __bit-or (__bit-or x y) more)))
+
+(defn bit-xor
+  ([x y] (__bit-xor x y))
+  ([x y & more] (reduce __bit-xor (__bit-xor x y) more)))
+
+(defn bit-and-not
+  ([x y] (__bit-and-not x y))
+  ([x y & more] (reduce __bit-and-not (__bit-and-not x y) more)))
+
 ;; The printing family, over two host seams: __write (push a string to *out*)
 ;; and __pr-str1 (render ONE value readably). The renderer itself stays host —
 ;; it's representation-coupled (pvec/phm/phs/sorted internals) and shared with