fix: correct biomechanical form across 14 movements

Form corrections from a movement-library review, keeping the spine neutral
under load, fully extending 'straight' limbs, and adding missing supporting-
foot ground-locks so single-leg poses don't drift:

- squat/box-squat/chair-pose: replace lumbar rounding (spine: flex) with a
  hip hinge + neutral/slightly-extended spine (real athletic squat form).
- forward-lunge: deepen the trailing knee (flex 45 -> 80) and add a small
  forward travel so it reads as a lunge, not a static split squat.
- bent-over-row: hang the arms from shoulder flex ~65 (arms vertical over a
  70-deg hinge) instead of shoulder extend 55, which threw them backward.
- pull-up: bring shoulders down toward the bar (flex 150 -> 105) during the
  pull instead of holding them locked overhead.
- crunch: reduce neck flex 20 -> 8 (less chin-tuck).
- seated-forward-fold: hinge at the hips (flex 90 -> 115) and cut spine flex
  60 -> 25 so it folds instead of slouching from the mid-back.
- bicycle-crunch/dead-bug: straighten the 'long' leg (knee ~5) and add chest
  counter-rotation so the twist reads.
- glute-bridge: raise hip extension 15 -> 20.
- single-leg-calf-raise/standing-hamstring-curl/standing-quad-stretch: add
  ground-lock: feet so the stance foot stays planted.

All ground-lock/pin changes use the real DSL vocab (groups 'hands'/'feet');
per-foot ground-lock names the reviewer suggested (foot_left) are not valid
ground-lock effectors, so supporting-foot locks use the feet group with the
existing near-floor planted-foot filter. 194 tests + 361/361 eval pass.

Author: a-baran-orhan

spec/examples/bent-over-row.posecode

@@ -5,28 +5,28 @@ posecode exercise "Bent-over row"
   step "Set the hinge" 1.6s ease-in-out:
     pelvis: hinge 70
     knees: flex 20
-    shoulders: extend 55
+    shoulders: flex 65
     elbows: flex 10
     neck: extend 12
     ground-lock: feet
     cue "Hinge to a flat back, let the arms hang straight down"
 
   step "Row" 0.9s ease-out:
-    shoulders: extend 15
+    shoulders: extend 10
     elbows: flex 95
     ground-lock: feet
     cue "Drive the elbows up past the ribs, squeeze the shoulder blades"
 
   step "Lower" 1s ease-in:
-    shoulders: extend 55
+    shoulders: flex 65
     elbows: flex 10
     ground-lock: feet
     cue "Lower the bar under control, keep the back flat"
 
   step "Stand" 1s ease-out:
     pelvis: hinge 0
     knees: flex 0
-    shoulders: extend 0
+    shoulders: flex 0
     elbows: flex 0
     neck: extend 0
     ground-lock: feet

spec/examples/bicycle-crunch.posecode

@@ -13,22 +13,25 @@ posecode exercise "Bicycle crunch"
 
   step "Right to left" 0.8s ease-in-out:
     spine: rotate-out 20
+    chest: rotate-out 12
     hip_left: flex 110
     knee_left: flex 90
-    hip_right: flex 25
-    knee_right: flex 20
+    hip_right: flex 15
+    knee_right: flex 5
     cue "Right elbow toward the left knee; the right leg extends long"
 
   step "Left to right" 0.8s ease-in-out:
     spine: rotate-in 20
+    chest: rotate-in 12
     hip_right: flex 110
     knee_right: flex 90
-    hip_left: flex 25
-    knee_left: flex 20
+    hip_left: flex 15
+    knee_left: flex 5
     cue "Switch: left elbow toward the right knee"
 
   step "Center" 0.6s ease-out:
     spine: rotate-in 0
+    chest: rotate-in 0
     hip_right: flex 90
     knee_right: flex 90
     hip_left: flex 90

spec/examples/box-squat.posecode

@@ -7,7 +7,8 @@ posecode exercise "Box squat"
     hips: flex 85
     knees: flex 90
     ankles: dorsiflex 12
-    spine: flex 10
+    pelvis: hinge 20
+    spine: flex 0
     shoulders: flex 70
     ground-lock: feet
     cue "Push the hips back and sit lightly onto the box"
@@ -16,6 +17,7 @@ posecode exercise "Box squat"
     hips: flex 0
     knees: flex 0
     ankles: dorsiflex 0
+    pelvis: hinge 0
     spine: flex 0
     shoulders: flex 0
     ground-lock: feet

spec/examples/chair-pose.posecode

@@ -7,7 +7,8 @@ posecode posture "Chair pose"
     knees: flex 70
     ankles: dorsiflex 12
     shoulders: flex 170
-    spine: flex 10
+    pelvis: hinge 15
+    spine: extend 5
     ground-lock: feet
     cue "Sit the hips back and down, reach the arms overhead"
 
@@ -16,7 +17,8 @@ posecode posture "Chair pose"
     knees: flex 0
     ankles: dorsiflex 0
     shoulders: flex 0
-    spine: flex 0
+    pelvis: hinge 0
+    spine: extend 0
     ground-lock: feet
     cue "Press through the feet to stand, arms float down"
 

spec/examples/crunch.posecode

@@ -7,7 +7,7 @@ posecode exercise "Crunch"
     knees: flex 90
     spine: flex 30
     chest: flex 20
-    neck: flex 20
+    neck: flex 8
     shoulders: flex 45
     ground-lock: feet
     cue "Curl the shoulders off the floor, ribs toward the hips"

spec/examples/dead-bug.posecode

@@ -10,17 +10,17 @@ posecode exercise "Dead bug"
 
   step "Extend right arm & left leg" 1.2s ease-in-out:
     shoulder_right: flex 150
-    hip_left: flex 25
-    knee_left: flex 30
+    hip_left: flex 20
+    knee_left: flex 5
     cue "Lower the right arm overhead and the left leg toward the floor"
 
   step "Switch" 1.2s ease-in-out:
     shoulder_right: flex 90
     hip_left: flex 90
     knee_left: flex 90
     shoulder_left: flex 150
-    hip_right: flex 25
-    knee_right: flex 30
+    hip_right: flex 20
+    knee_right: flex 5
     cue "Return and switch: left arm and right leg reach out"
 
   step "Return" 1s ease-out:

spec/examples/forward-lunge.posecode

@@ -6,9 +6,10 @@ posecode exercise "Forward lunge"
     hip_right: flex 45
     knee_right: flex 95
     hip_left: extend 15
-    knee_left: flex 45
+    knee_left: flex 80
     ankle_right: dorsiflex 14
     spine: extend 4
+    travel: 0 0.3
     ground-lock: feet
     cue "Step forward and lower the back knee toward the floor"
 
@@ -19,6 +20,7 @@ posecode exercise "Forward lunge"
     knee_left: flex 0
     ankle_right: dorsiflex 0
     spine: flex 0
+    travel: 0 0
     ground-lock: feet
     cue "Push through the front heel to stand tall"
 

spec/examples/glute-bridge.posecode

@@ -4,7 +4,7 @@ posecode exercise "Glute bridge"
 
   step "Bridge up" 1.6s ease-out:
     knees: flex 90
-    hips: extend 15
+    hips: extend 20
     spine: extend 10
     ground-lock: feet
     cue "Press through the feet and lift the hips toward the ceiling"

spec/examples/pull-up.posecode

@@ -16,7 +16,7 @@ posecode exercise "Pull-up"
     cue "Hang from the bar, arms long, shoulders active"
 
   step "Pull up" 1.2s ease-out:
-    shoulders: flex 150
+    shoulders: flex 105
     elbows: flex 130
     pin: hands bar
     cue "Pull the chest toward the bar, driving the elbows down"

spec/examples/seated-forward-fold.posecode

@@ -3,13 +3,15 @@ posecode stretch "Seated forward fold"
   pose start = seated
 
   step "Fold" 3s ease-in-out:
-    spine: flex 60
-    chest: flex 25
-    neck: flex 15
+    hips: flex 115
+    spine: flex 25
+    chest: flex 15
+    neck: flex 10
     shoulders: flex 60
     cue "Hinge forward from the hips over the legs, reaching toward the feet"
 
   step "Rise" 2.5s ease-in-out:
+    hips: flex 90
     spine: flex 0
     chest: flex 0
     neck: flex 0