Skip boundary.sx in component loader

boundary.sx files use define-page-helper which isn't an SX eval form —
they're parsed by boundary_parser.py. Exclude them from load_sx_dir()
to prevent EvalError on startup.

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

shared/sx/jinja_bridge.py

@@ -86,10 +86,15 @@ def _compute_component_hash() -> None:
 
 
 def load_sx_dir(directory: str) -> None:
-    """Load all .sx files from a directory and register components."""
+    """Load all .sx files from a directory and register components.
+
+    Skips boundary.sx — those are parsed separately by the boundary validator.
+    """
     for filepath in sorted(
         glob.glob(os.path.join(directory, "*.sx"))
     ):
+        if os.path.basename(filepath) == "boundary.sx":
+            continue
         with open(filepath, encoding="utf-8") as f:
             register_components(f.read())