feat(profiler/behave_shell): emit cognitive.planning_depth

Distribution of inter-command IATs bucketed against IKI_THINK_MAX_S
(deep) and INTER_CMD_INSTANT_MAX (reactive); fall-through is shallow.
v0.1 thresholds; D.8 re-tunes.

decnet/profiler/behave_shell/_features/__init__.py

@@ -16,6 +16,7 @@ from decnet.profiler.behave_shell._features.cognitive import (
     command_branch_diversity,
     exploration_style,
     feedback_loop_engagement,
+    planning_depth,
     inter_command_consistency,
     inter_command_latency_class,
 )
@@ -49,4 +50,5 @@ FEATURES: tuple[FeatureFn, ...] = (
     inter_command_consistency,
     cognitive_load,
     exploration_style,
+    planning_depth,
 )