Fix env-merge for Dict/Nil args + add adapter-html.sx primitives

sx_runtime.ml: unwrap_env now accepts Dict and Nil (converts to Env),
fixing env-merge when adapter-html.sx passes dict-as-env.

sx_server.ml + run_tests.ml: env-merge bindings use Sx_runtime.env_merge
(which handles Dict/Nil) instead of requiring strict Env pattern match.

sx_primitives.ml: Added scope stack (scope-push!/pop!/peek/emit!, emitted),
type predicates (lambda?/island?/component?/macro?), component accessors
(closure/name/params/body/has-children?), lambda accessors, for-each-indexed,
empty-dict?, make-raw-html, raw-html-content, is-else-clause?.

8 OCaml render tests still fail (env propagation in render-lambda-html) —
same adapter code works in JS and in production via Python bridge.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/ocaml/bin/run_tests.ml

@@ -208,7 +208,7 @@ let make_test_env () =
 
   bind "env-merge" (fun args ->
     match args with
-    | [Env a; Env b] -> Env (Sx_types.env_merge a b)
+    | [a; b] -> Sx_runtime.env_merge a b
     | _ -> raise (Eval_error "env-merge: expected 2 envs"));
 
   (* --- Equality --- *)
@@ -280,6 +280,11 @@ let make_test_env () =
   bind "eval-expr" (fun args ->
     match args with
     | [expr; Env e] -> eval_expr expr (Env e)
+    | [expr; Dict d] ->
+      (* Dict used as env — wrap it *)
+      let e = Sx_types.make_env () in
+      Hashtbl.iter (fun k v -> ignore (Sx_types.env_bind e k v)) d;
+      eval_expr expr (Env e)
     | [expr] -> eval_expr expr (Env env)
     | _ -> raise (Eval_error "eval-expr: expected (expr env)"));
   bind "scope-push!" (fun args ->