Rename multi-segment functions to two-concept names; polish docstrings

Naming pass: rename functions whose third+ segment is redundant or
implementation-detail, sticking to the codebase's preferred
``noun_verb`` / ``verb_noun`` two-concept idiom. Renames are atomic
across definitions, callers, and tests.

  is_penned_position        →  is_penned
  modulate_speed_near_sheep →  modulate_speed
  mecanum_kinematics_step   →  mecanum_step
  policy_forward_mean       →  forward_mean

Two-concept patterns like ``velocity_to_wheels`` / ``detections_from_scan``
/ ``make_strombom_predictor`` are left alone — they're idiomatic
converters / factories that read as a single concept, and the longer
form aids grep-ability.

Docstring polish:
* ``herding/config.py`` header drops the "previously lived as a
  module-level literal" historical framing — we ship as a single
  thing, so the refactor anecdote no longer earns its keep. The
  usage examples now mention both ``HERDING_WEBOTS`` and
  ``HERDING_MEC_WEBOTS`` presets.

126 pytest cases still pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

herding/control/active_scan.py

@@ -12,7 +12,7 @@ exploration behaviours:
   beyond the 12 m LiDAR range).
 
 When the tracker has detections the base teacher's action is used,
-post-processed by ``modulate_speed_near_sheep`` so the dog doesn't
+post-processed by ``modulate_speed`` so the dog doesn't
 charge the flock.
 """
 
@@ -20,7 +20,7 @@ from __future__ import annotations
 
 import math
 
-from herding.control.modulation import modulate_speed_near_sheep
+from herding.control.modulation import modulate_speed
 
 
 INITIAL_SCAN_STEPS = 80         # ≈1.3 s — covers one full rotation
@@ -117,6 +117,6 @@ class ActiveScanTeacher:
         else:
             vx, vy, mode = result
             omega = 0.0
-        vx, vy = modulate_speed_near_sheep(vx, vy, dog_xy, sheep_positions)
+        vx, vy = modulate_speed(vx, vy, dog_xy, sheep_positions)
         self.last_action = (vx, vy)
         return vx, vy, omega, mode