refactor: drop decnet- prefix — BEHAVE is now standalone

Rename packages and imports:
  decnet-behave-core  → behave-core
  decnet-behave-shell → behave-shell
  decnet-behave-text  → behave-text
  decnet_behave_*     → behave_*

BEHAVE is no longer a DECNET sub-project.

BEHAVE-SHELL/behave_shell/spec/event_adapter.py

@@ -0,0 +1,58 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+"""DECNET bus interop. Aligns BEHAVE Observation with DECNET Event payload shape.
+
+DECNET's Event (decnet/bus/base.py:26) carries ``(topic, payload, type, v, ts, id)``.
+A BEHAVE Observation maps onto that envelope as follows:
+
+    topic   = "attacker.observation." + observation.primitive
+    payload = observation.model_dump(exclude={"id", "ts", "v"})
+    type    = observation.primitive
+    v       = observation.v
+    ts      = observation.ts
+    id      = observation.id
+
+The publisher must set ``topic`` from the primitive when calling ``bus.publish()``;
+DECNET's bus does not trust topic from the wire (anti-spoofing, base.py:60-76).
+
+This module does NOT import DECNET. The adapter speaks dicts; consumers wire it
+to their own bus.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from .envelope import Observation
+
+TOPIC_PREFIX: str = "attacker.observation"
+
+
+def event_topic_for(primitive: str) -> str:
+    """Return the canonical DECNET bus topic for a BEHAVE primitive."""
+    return f"{TOPIC_PREFIX}.{primitive}"
+
+
+def to_event_payload(obs: Observation) -> dict[str, Any]:
+    """Project an Observation into a dict suitable for ``Event.payload``.
+
+    Excludes ``id``, ``ts``, and ``v`` because those are carried at the Event
+    envelope level by DECNET, not in the payload body.
+    """
+    return obs.model_dump(exclude={"id", "ts", "v"}, mode="json")
+
+
+def from_event_payload(primitive: str, payload: dict[str, Any]) -> Observation:
+    """Reconstruct an Observation from ``(topic-derived primitive, Event.payload)``.
+
+    The ``primitive`` argument is the trailing segment of the bus topic, NOT a
+    field read from the payload — relying on the wire-side ``primitive`` field
+    would let a misbehaving publisher spoof observations on topics they don't
+    actually publish to. This mirrors DECNET's ``Event.from_dict`` discipline
+    (decnet/bus/base.py:60-76).
+    """
+    if "primitive" in payload and payload["primitive"] != primitive:
+        raise ValueError(
+            f"payload.primitive ({payload['primitive']!r}) does not match "
+            f"topic-derived primitive ({primitive!r}); refusing to reconstruct"
+        )
+    return Observation.model_validate({**payload, "primitive": primitive})