Phase 13: Protocol Completion — reify dispatch, #() reader, IFn protocol

- reader.janet: rewrite read-anon-fn to handle % arg references
  % → gensym, %1/%2 → sorted gensyms, replaces all matching % refs
- evaluator.janet: IFn protocol support in default invocation arm
  Before erroring "Cannot call X as a function", checks for:
  1) type-registry IFn/-invoke method (extend-type protocols)
  2) :jolt/protocol-methods :-invoke (reified objects)
- test/phase13-test.janet: 4 test sections (28-31)
  28: reify dispatch — protocol methods on reified objects
  29: #() anon-fn — % and %1/%2 arg handling
  30: extend-type — protocol method dispatch for deftypes
  31: clojure.walk loading — keywordize-keys loads correctly
- All pass: 316 ok, 1 fail (pre-existing, unchanged)

test/phase13-test.janet

@@ -0,0 +1,44 @@
+(use ../src/jolt/api)
+(use ../src/jolt/evaluator)
+(use ../src/jolt/reader)
+(defn ct-eval [ctx s] (eval-string ctx s))
+
+(defn load-clj [ctx filepath]
+  (var s (slurp filepath))
+  (while (> (length (string/trim s)) 0)
+    (def [form rest] (parse-next s))
+    (set s rest)
+    (when (not (nil? form))
+      (eval-form ctx @{} form))))
+
+(print "=== Phase 13: Protocol Completion ===")
+
+(print "28: reify dispatch...")
+(let [ctx (init)]
+  (ct-eval ctx "(defprotocol Greeter (say-hello [this]))")
+  (ct-eval ctx "(def r (reify Greeter (say-hello [this] \"hello reify\")))")
+  (assert (= "hello reify" (ct-eval ctx "(say-hello r)")) "reify dispatch"))
+(print "  ok")
+
+(print "29: #() anon-fn reader...")
+(let [ctx (init)]
+  (assert (= 2 (ct-eval ctx "(#(inc %) 1)")) "anon fn %")
+  (assert (= 3 (ct-eval ctx "(#(+ %1 %2) 1 2)")) "anon fn %1 %2")
+  (assert (= [1 2 3] (ct-eval ctx "(map #(inc %) [0 1 2])")) "anon fn map"))
+(print "  ok")
+
+(print "30: extend-type full dispatch...")
+(let [ctx (init)]
+  (ct-eval ctx "(defprotocol Greet (g [this]))")
+  (ct-eval ctx "(deftype Dog [name])")
+  (ct-eval ctx "(extend-type Dog Greet (g [this] (str \"woof \" (.-name this))))")
+  (assert (= "woof Rex" (ct-eval ctx "(g (Dog. \"Rex\"))")) "extend-type dog"))
+(print "  ok")
+
+(print "31: clojure.walk loading...")
+(let [ctx (init)]
+  (load-clj ctx "src/jolt/clojure/walk.clj")
+  (assert (function? (ct-eval ctx "keywordize-keys")) "keywordize-keys is fn"))
+(print "  ok")
+
+(print "\nAll Phase 13 tests passed!")