feat(profiler/behave_shell): emit environmental.locale

Searches ANSI-stripped output for LANG / LC_ALL / LC_CTYPE envvar
substrings emitted by env / locale / printenv. Highest-priority key
wins (LC_ALL > LANG > LC_CTYPE); POSIX value normalised to BCP-47:
en_US.UTF-8 → en-US, pt_BR.UTF-8 → pt-BR, C/POSIX → und. Free-string
registry value emitted directly.

PII discipline: only the parsed locale value enters observations;
surrounding output is read once for matching and dropped.

decnet/profiler/behave_shell/_features/__init__.py

@@ -25,6 +25,7 @@ from decnet.profiler.behave_shell._features.cognitive import (
     inter_command_latency_class,
 )
 from decnet.profiler.behave_shell._features.environmental import (
+    locale,
     shell_type,
     terminal_multiplexer,
 )
@@ -73,4 +74,5 @@ FEATURES: tuple[FeatureFn, ...] = (
     landing_ritual,
     shell_type,
     terminal_multiplexer,
+    locale,
 )