Move stdlib out of spec — clean spec/library boundary

spec/ now contains only the language definition (5 files):
  evaluator.sx, parser.sx, primitives.sx, render.sx, special-forms.sx

lib/ contains code written IN the language (8 files):
  stdlib.sx, types.sx, freeze.sx, content.sx,
  bytecode.sx, compiler.sx, vm.sx, callcc.sx

Test files follow source: spec/tests/ for core language tests,
lib/tests/ for library tests (continuations, freeze, types, vm).

Updated all consumers:
- JS/Python/OCaml bootstrappers: added lib/ to source search paths
- OCaml bridge: spec_dir for parser/render, lib_dir for compiler/freeze
- JS test runner: scans spec/tests/ (always) + lib/tests/ (--full)
- OCaml test runner: scans spec/tests/, lib tests via explicit request
- Docker dev mounts: added ./lib:/app/lib:ro

Tests: 1041 JS standard, 1322 JS full, 1101 OCaml — all pass

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

docker-compose.dev-sx.yml

@@ -31,8 +31,9 @@ services:
       - ./sx/sx:/app/sx
       - ./sx/path_setup.py:/app/path_setup.py
       - ./sx/entrypoint.sh:/usr/local/bin/entrypoint.sh
-      # Spec + web SX files (loaded by OCaml kernel for aser, parser, render)
+      # Spec + lib + web SX files (loaded by OCaml kernel)
       - ./spec:/app/spec:ro
+      - ./lib:/app/lib:ro
       - ./web:/app/web:ro
       # OCaml SX kernel binary (built with: cd hosts/ocaml && eval $(opam env) && dune build)
       - ./hosts/ocaml/_build/default/bin/sx_server.exe:/app/bin/sx_server:ro