Step 5 piece 6: migrate 23 .sx files to define-library/import

Wraps all core .sx files in R7RS define-library with explicit export
lists, plus (import ...) at end for backward-compatible global re-export.

Libraries registered:
  (sx bytecode)      — 83 opcode constants
  (sx render)        — 15 tag registries + render helpers
  (sx signals)       — 23 reactive signal primitives
  (sx r7rs)          — 21 R7RS aliases
  (sx compiler)      — 42 compiler functions
  (sx vm)            — 32 VM functions
  (sx freeze)        — 9 freeze/thaw functions
  (sx content)       — 6 content store functions
  (sx callcc)        — 1 call/cc wrapper
  (sx highlight)     — 13 syntax highlighting functions
  (sx stdlib)        — 47 stdlib functions
  (sx swap)          — 13 swap algebra functions
  (sx render-trace)  — 8 render trace functions
  (sx harness)       — 21 test harness functions
  (sx canonical)     — 12 canonical serialization functions
  (web adapter-html) — 13 HTML renderer functions
  (web adapter-sx)   — 13 SX wire format functions
  (web engine)       — 33 hypermedia engine functions
  (web request-handler) — 4 request handling functions
  (web page-helpers) — 12 page helper functions
  (web router)       — 36 routing functions
  (web deps)         — 19 dependency analysis functions
  (web orchestration) — 59 page orchestration functions

Key changes:
- define-library now inherits parent env (env-extend env instead of
  env-extend make-env) so library bodies can access platform primitives
- sx_server.ml: added resolve_library_path + load_library_file for
  import resolution (maps library specs to file paths)
- cek_run_with_io: handles "import" locally instead of sending to
  Python bridge

2608/2608 tests passing.

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

hosts/ocaml/lib/sx_ref.ml

@@ -503,7 +503,7 @@ and step_eval_list expr env kont =
 
 (* step-sf-define-library *)
 and step_sf_define_library args env kont =
-  (let lib_spec = (first (args)) in let decls = (rest (args)) in (let lib_env = (env_extend ((make_env ()))) in let exports = ref ((List [])) in let body_forms = ref ((List [])) in (let () = ignore ((List.iter (fun decl -> ignore ((if sx_truthy ((let _and = (list_p (decl)) in if not (sx_truthy _and) then _and else (let _and = (Bool (not (sx_truthy ((empty_p (decl)))))) in if not (sx_truthy _and) then _and else (symbol_p ((first (decl))))))) then (let kind = (symbol_name ((first (decl)))) in (if sx_truthy ((prim_call "=" [kind; (String "export")])) then (exports := (prim_call "append" [!exports; (List (List.map (fun s -> (if sx_truthy ((symbol_p (s))) then (symbol_name (s)) else (String (sx_str [s])))) (sx_to_list (rest (decl)))))]); Nil) else (if sx_truthy ((prim_call "=" [kind; (String "begin")])) then (body_forms := (prim_call "append" [!body_forms; (rest (decl))]); Nil) else Nil))) else Nil))) (sx_to_list decls); Nil)) in (let () = ignore ((List.iter (fun form -> ignore ((eval_expr (form) (lib_env)))) (sx_to_list !body_forms); Nil)) in (let export_dict = (Dict (Hashtbl.create 0)) in (let () = ignore ((List.iter (fun name -> ignore ((if sx_truthy ((env_has (lib_env) (name))) then (sx_dict_set_b export_dict name (env_get (lib_env) (name))) else Nil))) (sx_to_list !exports); Nil)) in (let () = ignore ((register_library (lib_spec) (export_dict))) in (make_cek_value (Nil) (env) (kont)))))))))
+  (let lib_spec = (first (args)) in let decls = (rest (args)) in (let lib_env = (env_extend (env)) in let exports = ref ((List [])) in let body_forms = ref ((List [])) in (let () = ignore ((List.iter (fun decl -> ignore ((if sx_truthy ((let _and = (list_p (decl)) in if not (sx_truthy _and) then _and else (let _and = (Bool (not (sx_truthy ((empty_p (decl)))))) in if not (sx_truthy _and) then _and else (symbol_p ((first (decl))))))) then (let kind = (symbol_name ((first (decl)))) in (if sx_truthy ((prim_call "=" [kind; (String "export")])) then (exports := (prim_call "append" [!exports; (List (List.map (fun s -> (if sx_truthy ((symbol_p (s))) then (symbol_name (s)) else (String (sx_str [s])))) (sx_to_list (rest (decl)))))]); Nil) else (if sx_truthy ((prim_call "=" [kind; (String "begin")])) then (body_forms := (prim_call "append" [!body_forms; (rest (decl))]); Nil) else Nil))) else Nil))) (sx_to_list decls); Nil)) in (let () = ignore ((List.iter (fun form -> ignore ((eval_expr (form) (lib_env)))) (sx_to_list !body_forms); Nil)) in (let export_dict = (Dict (Hashtbl.create 0)) in (let () = ignore ((List.iter (fun name -> ignore ((if sx_truthy ((env_has (lib_env) (name))) then (sx_dict_set_b export_dict name (env_get (lib_env) (name))) else Nil))) (sx_to_list !exports); Nil)) in (let () = ignore ((register_library (lib_spec) (export_dict))) in (make_cek_value (Nil) (env) (kont)))))))))
 
 (* bind-import-set *)
 and bind_import_set import_set env =