Add deftype and defeffect to SX type system (Phases 6-7)

Phase 6 — deftype: named type aliases, unions, records, and parameterized
types. Type definitions stored as plain dicts in *type-registry*. Includes
resolve-type for named type resolution, substitute-type-vars for
parameterized instantiation, subtype-resolved? for structural record
subtyping, and infer-type extension for record field type inference via get.

Phase 7 — defeffect: static effect annotations. Effects stored in
*effect-registry* and *effect-annotations*. Supports :effects keyword on
defcomp and define. Gradual: unannotated = all effects, empty list = pure.
check-body-walk validates effect containment at call sites.

Standard types defined: (maybe a), type-def, diagnostic, prim-param-sig.
Standard effects declared: io, mutation, render.

84/84 type system tests pass. Both Python and JS bootstrappers succeed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/adapter-sx.sx

@@ -170,7 +170,8 @@
         "define" "defcomp" "defmacro" "defstyle"
         "defhandler" "defpage" "defquery" "defaction" "defrelation"
         "begin" "do" "quote" "quasiquote"
-        "->" "set!" "letrec" "dynamic-wind" "defisland"))
+        "->" "set!" "letrec" "dynamic-wind" "defisland"
+        "deftype" "defeffect"))
 
 (define HO_FORM_NAMES
   (list "map" "map-indexed" "filter" "reduce"
@@ -304,7 +305,8 @@
         ;; Definition forms — evaluate for side effects
         (or (= name "define") (= name "defcomp") (= name "defmacro")
             (= name "defstyle") (= name "defhandler") (= name "defpage")
-            (= name "defquery") (= name "defaction") (= name "defrelation"))
+            (= name "defquery") (= name "defaction") (= name "defrelation")
+            (= name "deftype") (= name "defeffect"))
           (do (trampoline (eval-expr expr env)) nil)
 
         ;; Everything else — evaluate normally