perf(1.1): lazy topology.generate re-export (C2)

topology/__init__ eagerly imported generator -> allocator -> repository ->
the full SQLModel ORM. Defer via PEP 562 __getattr__ so importing the
package doesn't drag the DB layer into DB-less workers. Public API
(from decnet.topology import generate) unchanged. Guard test locks it in.

decnet/topology/__init__.py

@@ -7,7 +7,6 @@ is marked as the DMZ (Internet-facing).  Persisted via the repo pattern;
 deployed via :mod:`decnet.engine.deployer`.
 """
 from decnet.topology.config import TopologyConfig, GeneratedTopology
-from decnet.topology.generator import generate
 from decnet.topology.status import (
     TopologyStatus,
     assert_transition,
@@ -22,3 +21,14 @@ __all__ = [
     "assert_transition",
     "TopologyStatusError",
 ]
+
+
+def __getattr__(name: str):
+    # ponytail: lazy re-export — `generate` pulls generator→allocator→repository→the
+    # full SQLModel ORM (~38MB). Defer it so importing this package (which every worker
+    # does transitively via the CLI) doesn't drag the DB layer into DB-less workers.
+    if name == "generate":
+        from decnet.topology.generator import generate
+
+        return generate
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")