Phase 1: s-expression core library + test infrastructure

S-expression parser, evaluator, and primitive registry in shared/sexp/.
109 unit tests covering parsing, evaluation, special forms, lambdas,
closures, components (defcomp), and 60+ pure builtins.

Test infrastructure: Dockerfile.unit (tier 1, fast) and
Dockerfile.integration (tier 2, ffmpeg). Dev watch mode auto-reruns
on file changes. Deploy gate blocks push on test failure.

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

dev.sh

@@ -20,6 +20,24 @@ case "${1:-up}" in
     shift
     $COMPOSE logs -f "$@"
     ;;
+  test)
+    # One-shot: all unit tests
+    $COMPOSE run --rm test-unit python -m pytest \
+      shared/ artdag/core/tests/ artdag/core/artdag/sexp/ \
+      artdag/l1/tests/ artdag/l1/sexp_effects/ \
+      -v --tb=short \
+      --ignore=artdag/l1/tests/test_jax_primitives.py \
+      --ignore=artdag/l1/tests/test_jax_pipeline_integration.py \
+      -k "not gpu and not cuda"
+    ;;
+  test-integration)
+    # One-shot: integration tests (needs ffmpeg, heavier)
+    $COMPOSE run --rm test-integration
+    ;;
+  watch)
+    # Auto-rerun unit tests on file changes (stays running)
+    $COMPOSE up test-unit
+    ;;
   build)
     shift
     if [[ $# -eq 0 ]]; then