fix: reach (not ground-lock) for relocating feet in single-leg/turn moves

Same fix as the gait closing steps, applied to more moves that declared a
moving foot as a planted support:

- high-knee-march: the descending knee-drive foot ("Switch") and the returning
  feet ("Down") are landing, not planted (was 0.40m planted-drift).
- hip-abduction, hip-flexion-demo: the raised leg's foot lands during "Lower".
- front-kick "Return", tendu "Close through the floor": the working foot
  returns/brushes home while the other stays planted.
- box-step-taps "Right/Left down": the tapping foot lands.
- quarter-turns: feet pivot to the new facing on each 90° turn (was 0.19m
  orbit-drift), like walk-cycle's about-face.

Each keeps the true stance foot ground-locked and declares the moving foot a
`reach: foot floor`. high-knee-march, hip-abduction, hip-flexion-demo,
front-kick, tendu, quarter-turns are now warning-free.

Eval: 1555/1555 checks both proportions; constraint warnings 146 -> 125.
397/397 tests pass.

Author: a-baran-orhan

spec/examples/box-step-taps.posecode

@@ -14,7 +14,8 @@ posecode exercise "Box step taps"
     hip_right: flex 0
     knee_right: flex 0
     ankle_right: plantarflex 0
-    ground-lock: feet
+    ground-lock: foot_left
+    reach: foot_right floor
     cue "Return the right foot to the floor"
 
   step "Left tap" 0.6s settle:
@@ -28,7 +29,8 @@ posecode exercise "Box step taps"
     hip_left: flex 0
     knee_left: flex 0
     ankle_left: plantarflex 0
-    ground-lock: feet
+    ground-lock: foot_right
+    reach: foot_left floor
     cue "Back to the floor: keep a light, quick rhythm"
 
   repeat 6

spec/examples/front-kick.posecode

@@ -23,7 +23,8 @@ posecode exercise "Front kick"
   step "Return" 0.6s settle:
     hip_right: flex 0
     knee_right: flex 0
-    ground-lock: feet
+    ground-lock: foot_left
+    reach: foot_right floor
     cue "Set the foot back down to a fighting stance"
 
   repeat 5

spec/examples/high-knee-march.posecode

@@ -16,14 +16,15 @@ posecode exercise "High-knee march"
     hip_left: flex 90
     knee_left: flex 90
     shoulder_right: flex 40
-    pin: foot_right floor
+    reach: foot_right floor
     cue "Plant and drive the left knee up"
 
   step "Down" 0.6s settle:
     hip_left: flex 0
     knee_left: flex 0
     shoulder_right: flex 0
-    ground-lock: feet
+    reach: foot_left floor
+    reach: foot_right floor
     cue "Return to a tall, ready stance"
 
   repeat 6

spec/examples/hip-abduction.posecode

@@ -9,7 +9,8 @@ posecode exercise "Standing hip abduction"
 
   step "Lower" 1.6s settle:
     hip_right: abduct 0
-    ground-lock: feet
+    ground-lock: foot_left
+    reach: foot_right floor
     cue "Lower the leg back to the midline"
 
   repeat 10

spec/examples/hip-flexion-demo.posecode

@@ -9,7 +9,8 @@ posecode stretch "Hip flexion (ROM demo)"
 
   step "Lower" 2.5s settle:
     hip_right: flex 0
-    ground-lock: feet
+    ground-lock: foot_left
+    reach: foot_right floor
     cue "Lower the leg back under the hip"
 
   repeat 4

spec/examples/quarter-turns.posecode

@@ -8,7 +8,8 @@ posecode posture "Quarter turns"
     ankles: plantarflex 20
     shoulders: abduct 30
     turn: 90
-    ground-lock: feet
+    reach: foot_left floor
+    reach: foot_right floor
     cue "Small dip and pivot a quarter-turn to the right"
 
   step "Face back" 1s flow:
@@ -17,7 +18,8 @@ posecode posture "Quarter turns"
     ankles: plantarflex 0
     shoulders: abduct 0
     turn: 180
-    ground-lock: feet
+    reach: foot_left floor
+    reach: foot_right floor
     cue "Rise, then pivot another quarter-turn to face the back"
 
   step "Face left" 1s flow:
@@ -26,7 +28,8 @@ posecode posture "Quarter turns"
     ankles: plantarflex 20
     shoulders: abduct 30
     turn: 270
-    ground-lock: feet
+    reach: foot_left floor
+    reach: foot_right floor
     cue "Dip and pivot again to face the far side"
 
   step "Face front" 1s settle:
@@ -35,7 +38,8 @@ posecode posture "Quarter turns"
     ankles: plantarflex 0
     shoulders: abduct 0
     turn: 360
-    ground-lock: feet
+    reach: foot_left floor
+    reach: foot_right floor
     cue "Rise and complete the circle, back to front"
 
   repeat 3

spec/examples/tendu.posecode

@@ -18,7 +18,8 @@ posecode exercise "Tendu"
     ankle_right: plantarflex 0
     shoulders: abduct 0
     elbows: flex 0
-    ground-lock: feet
+    ground-lock: foot_left
+    reach: foot_right floor
     cue "Draw the foot back to first position, heel down"
 
   repeat 4