Phase 12: Protocol System — full implementation with all tests passing

Root cause: fn* multi-arity detection checks (array? (in form 1))
— defprotocol used @[...] for args, triggering multi-arity path
that treated the body form as a second arity pair.

Fixes applied:
- defprotocol: change fn* args from @[...] to [...] (tuple)
  so single-arity fn* path is used with [this & rest-args]
- defprotocol: remove quote wrappers from protocol-dispatch call
  (protocol-name and method-name passed directly as symbols)
- extend-type/extend-protocol: remove quote wrappers from
  register-method call (symbols passed directly, not via quote)
- protocol-dispatch: use (in form ...) directly for proto/method
  symbols (no eval-form needed after quote removal)
- satisfy?: extract name string from protocol value's :name field
  (which is a symbol struct, not a plain string)
- make-reified: remove spurious (apply fn []) call
- core-reify: fix (keyword struct) → extract :name string first
- core-extend-protocol: handle single method spec vs multi

5 test sections (35-39) covering:
  defprotocol, extend-type, extend-protocol,
  satisfies?, reify — all pass

315 ok, 2 fail (pre-existing, unchanged)

test/phase12-test.janet

@@ -0,0 +1,50 @@
+# Phase 12: Protocol System Tests
+(use ../src/jolt/api)
+(defn ct-eval [ctx s] (eval-string ctx s))
+
+(print "35: defprotocol...")
+(let [ctx (init)]
+  (ct-eval ctx "(defprotocol Greet (greet [this]))")
+  (let [p (ct-eval ctx "Greet")]
+    (assert (not (nil? p)) "protocol var exists")
+    (assert (= :jolt/protocol (get p :jolt/type)) "protocol type tag")
+    (assert (get (get p :methods) :greet) "protocol has greet method"))
+  (assert (or (function? (ct-eval ctx "greet")) (cfunction? (ct-eval ctx "greet"))) "method fn exists"))
+(print "  passed")
+
+(print "36: extend-type...")
+(let [ctx (init)]
+  (ct-eval ctx "(deftype Person [name])")
+  (ct-eval ctx "(defprotocol Namable (get-name [this]))")
+  (ct-eval ctx "(extend-type Person Namable (get-name [this] (.-name this)))")
+  (assert (= "Alice" (ct-eval ctx "(get-name (Person. \"Alice\"))")) "extend-type works"))
+(print "  passed")
+
+(print "37: extend-protocol...")
+(let [ctx (init)]
+  (ct-eval ctx "(deftype Dog [breed])")
+  (ct-eval ctx "(deftype Cat [color])")
+  (ct-eval ctx "(defprotocol Animal (speak [this]))")
+  (ct-eval ctx "(extend-protocol Animal
+    Dog (speak [this] (str \"woof from \" (.-breed this)))
+    Cat (speak [this] (str \"meow from \" (.-color this))))")
+  (assert (= "woof from poodle" (ct-eval ctx "(speak (Dog. \"poodle\"))")) "dog speak")
+  (assert (= "meow from black" (ct-eval ctx "(speak (Cat. \"black\"))")) "cat speak"))
+(print "  passed")
+
+(print "38: satisfies?...")
+(let [ctx (init)]
+  (ct-eval ctx "(deftype Point [x y])")
+  (ct-eval ctx "(defprotocol Locatable (location [this]))")
+  (ct-eval ctx "(extend-type Point Locatable (location [this] [(.-x this) (.-y this)]))")
+  (assert (= true (ct-eval ctx "(satisfies? Locatable (Point. 3 4))")) "satisfies? true")
+  (assert (= false (ct-eval ctx "(satisfies? Locatable {:x 1})")) "satisfies? false"))
+(print "  passed")
+
+(print "39: reify...")
+(let [ctx (init)]
+  (ct-eval ctx "(defprotocol Stringable (to-str [this]))")
+  (assert (= "works" (ct-eval ctx "(to-str (reify Stringable (to-str [this] \"works\")))")) "reify single method"))
+(print "  passed")
+
+(print "\nAll Phase 12 tests passed!")