refactor(cdsl_engine): executor registry + per-family executor package

Phase 3 of the decoupling refactor (behavior-preserving):
- registry.py: atomic_executor decorator, ALL_ATOMIC_IDS with
  fail-fast registration validation, execute_node dispatcher
- executors/: one module per family (extrude, revolve, surfaces,
  loft_sweep, bodies, context, primitives, parametric, holes,
  dressup, patterns) + shared helpers in executors/common
- executors/__init__: explicit aggregation + completeness check
  (registry must cover every declared atomic id at import time)
- runtime.py: slimmed to entry points (analyze_cdsl/rebuild_cdsl)
  plus full historical re-exports incl. test-referenced privates

Adding an atomic operation now touches only one executor module and
its schema contract; the shared registry never changes. Verified
against baseline: zero new failures.

backend/engine/cdsl_engine/executors/revolve.py

@@ -0,0 +1,17 @@
+"""Revolution solid executors (revolve_add / revolve_cut)."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Any
+
+from ..registry import atomic_executor
+from ..topology import FeaturePlanNode, FeatureResult
+from .common import _shape_from_primary
+
+if TYPE_CHECKING:  # pragma: no cover - import for type checkers only
+    from ..session import ExecutionSession
+
+
+@atomic_executor("revolve_add", "revolve_cut")
+def _primary_executor(node: FeaturePlanNode, session: "ExecutionSession", sketch: dict[str, Any] | None) -> FeatureResult:
+    return _shape_from_primary(node, session, sketch=sketch)