Separate core spec from web framework

Three-layer architecture:
  spec/  — Core language (19 files): evaluator, parser, primitives,
           CEK machine, types, continuations. Host-independent.
  web/   — Web framework (20 files): signals, adapters, engine,
           orchestration, boot, router, CSSX. Built on core spec.
  sx/    — Application (sx-docs website). Built on web framework.

Split boundary.sx into boundary-core.sx (type-of, make-env, identical?)
and boundary-web.sx (IO primitives, signals, spreads, page helpers).

Bootstrappers search spec/ → web/ → shared/sx/ref/ for .sx files.
Original files remain in shared/sx/ref/ as fallback during transition.
All 63 tests pass.

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

shared/sx/ref/run_js_sx.py

@@ -78,6 +78,13 @@ def compile_ref_to_js(
     from shared.sx.ref.sx_ref import evaluate
 
     ref_dir = _HERE
+    _PROJECT = os.path.abspath(os.path.join(_HERE, "..", "..", ".."))
+    # Source directories: core spec, web framework, and legacy ref (for bootstrapper tools)
+    _source_dirs = [
+        os.path.join(_PROJECT, "spec"),      # Core spec
+        os.path.join(_PROJECT, "web"),        # Web framework
+        ref_dir,                              # Legacy location (fallback)
+    ]
     env = load_js_sx()
 
     # Resolve adapter set
@@ -195,9 +202,16 @@ def compile_ref_to_js(
         parts.append(PLATFORM_CEK_JS)
 
     # Translate each spec file using js.sx
+    def _find_sx(filename):
+        for d in _source_dirs:
+            p = os.path.join(d, filename)
+            if os.path.exists(p):
+                return p
+        return None
+
     for filename, label in sx_files:
-        filepath = os.path.join(ref_dir, filename)
-        if not os.path.exists(filepath):
+        filepath = _find_sx(filename)
+        if not filepath:
             continue
         with open(filepath) as f:
             src = f.read()