Document SX rendering pipeline, add missing sx_docs mount, loud error on missing component

- CLAUDE.md: add SX rendering pipeline overview, service sx/ vs sxc/
  convention, dev container mount convention
- docker-compose.dev.yml: add missing ./sx/sx:/app/sx bind mount for
  sx_docs (root cause of "Unknown component: ~sx-layout-full")
- async_eval.py: add evaluation modes table to module docstring; log
  error when async_eval_slot_to_sx can't find a component instead of
  silently falling through to client-side serialization
- helpers.py: remove debug logging from render_to_sx_with_env

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

docker-compose.dev.yml

@@ -399,6 +399,7 @@ services:
       - ./sx/bp:/app/bp
       - ./sx/services:/app/services
       - ./sx/content:/app/content
+      - ./sx/sx:/app/sx
       - ./sx/path_setup.py:/app/path_setup.py
       - ./sx/entrypoint.sh:/usr/local/bin/entrypoint.sh
       - ./sx/__init__.py:/app/__init__.py:ro