feat(profiler/behave_shell): emit temporal.session_duration

Bucket ctx.duration_s against SESSION_DURATION_SHORT_MAX (60s) /
MEDIUM_MAX (600s) / LONG_MAX (3600s); else marathon. Direct
measurement, confidence 0.85. Skip emission only when no commands
and zero duration. New _features/temporal.py module opens Phase E.

decnet/profiler/behave_shell/_features/__init__.py

@@ -24,6 +24,9 @@ from decnet.profiler.behave_shell._features.cognitive import (
     inter_command_consistency,
     inter_command_latency_class,
 )
+from decnet.profiler.behave_shell._features.temporal import (
+    session_duration,
+)
 from decnet.profiler.behave_shell._features.motor import (
     command_chunking,
     error_correction,
@@ -59,4 +62,5 @@ FEATURES: tuple[FeatureFn, ...] = (
     error_resilience_retry_tactic,
     error_resilience_frustration_typing,
     error_resilience_fallback_to_man,
+    session_duration,
 )