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>

tests/test_diffdrive.py

@@ -6,7 +6,7 @@ import pytest
 
 from herding.world.diffdrive import (
     heading_speed_to_wheels, kinematics_step,
-    mecanum_inverse, mecanum_kinematics_step,
+    mecanum_inverse, mecanum_step,
     velocity_to_mecanum_wheels, velocity_to_wheels,
 )
 
@@ -95,7 +95,7 @@ LY = 0.14   # half wheel_base_y
 
 
 def test_mecanum_kinematics_zero_is_identity():
-    x, y, h = mecanum_kinematics_step(
+    x, y, h = mecanum_step(
         1.0, 2.0, 0.5, 0.0, 0.0, 0.0, 0.0, WHEEL_R, LX, LY, DT,
     )
     assert (x, y, h) == (1.0, 2.0, 0.5)
@@ -104,7 +104,7 @@ def test_mecanum_kinematics_zero_is_identity():
 def test_mecanum_kinematics_pure_forward():
     # All 4 wheels equal → pure forward (vx_body > 0, vy_body = 0).
     w = 10.0
-    x, y, h = mecanum_kinematics_step(
+    x, y, h = mecanum_step(
         0.0, 0.0, 0.0, w, w, w, w, WHEEL_R, LX, LY, DT,
     )
     assert h == pytest.approx(0.0, abs=1e-9)
@@ -118,7 +118,7 @@ def test_mecanum_kinematics_pure_strafe():
     # vy_body = (-w_fl+w_fr+w_rl-w_rr)*r/4 > 0
     # Use w_fl=-10, w_fr=10, w_rl=10, w_rr=-10.
     w_fl, w_fr, w_rl, w_rr = -10.0, 10.0, 10.0, -10.0
-    x, y, h = mecanum_kinematics_step(
+    x, y, h = mecanum_step(
         0.0, 0.0, 0.0, w_fl, w_fr, w_rl, w_rr, WHEEL_R, LX, LY, DT,
     )
     assert h == pytest.approx(0.0, abs=1e-9)
@@ -130,7 +130,7 @@ def test_mecanum_kinematics_pure_strafe():
 def test_mecanum_kinematics_strafe_efficiency_scales_y():
     # With strafe_efficiency=0.4, realised strafe should be 40% of ideal.
     w_fl, w_fr, w_rl, w_rr = -10.0, 10.0, 10.0, -10.0
-    x, y, _ = mecanum_kinematics_step(
+    x, y, _ = mecanum_step(
         0.0, 0.0, 0.0, w_fl, w_fr, w_rl, w_rr, WHEEL_R, LX, LY, DT,
         strafe_efficiency=0.4,
     )
@@ -142,7 +142,7 @@ def test_mecanum_kinematics_strafe_efficiency_scales_y():
 def test_mecanum_kinematics_strafe_bleed_pushes_backward():
     # Negative bleed means strafe commands also push the body backward.
     w_fl, w_fr, w_rl, w_rr = -10.0, 10.0, 10.0, -10.0
-    x, y, _ = mecanum_kinematics_step(
+    x, y, _ = mecanum_step(
         0.0, 0.0, 0.0, w_fl, w_fr, w_rl, w_rr, WHEEL_R, LX, LY, DT,
         strafe_efficiency=1.0,
         strafe_to_forward_bleed=-0.28,
@@ -156,7 +156,7 @@ def test_mecanum_kinematics_strafe_bleed_pushes_backward():
 def test_mecanum_kinematics_forward_unaffected_by_strafe_params():
     # Forward command should be untouched by strafe_efficiency / bleed.
     w_fl = w_fr = w_rl = w_rr = 10.0
-    x, y, _ = mecanum_kinematics_step(
+    x, y, _ = mecanum_step(
         0.0, 0.0, 0.0, w_fl, w_fr, w_rl, w_rr, WHEEL_R, LX, LY, DT,
         strafe_efficiency=0.4,
         strafe_to_forward_bleed=-0.28,
@@ -170,7 +170,7 @@ def test_mecanum_kinematics_pure_rotation():
     # Pure rotation: vx_body=0, vy_body=0, omega>0.
     # w_fl=-10, w_fr=10, w_rl=-10, w_rr=10 → all sums cancel except omega.
     w_fl, w_fr, w_rl, w_rr = -10.0, 10.0, -10.0, 10.0
-    x, y, h = mecanum_kinematics_step(
+    x, y, h = mecanum_step(
         0.0, 0.0, 0.0, w_fl, w_fr, w_rl, w_rr, WHEEL_R, LX, LY, DT,
     )
     assert x == pytest.approx(0.0, abs=1e-9)