exp(vagrant): try procedural lower-body, drop WASD-to-root coupling

- humanoid.rig.json: removed locomotion-block (apply_locomotion no-ops
  now). head: removed look_at_speed (instant snap). body: unchanged
  (look_at_speed=180 lazy).
- init.lua: removed set_procedural("facing", ...) — root stays at
  rest.rot=0. walk.anim + idle_lower.anim no longer loaded/played
  (files retained on disk for revert). New set_procedural("walk_cycle",
  ...) drives legs per-frame: walk_phase advances at 1.25Hz, sin-cycle
  on leg.scl, walk_dir applied to leg.rot. Idle: legs scl=0.
- Lazy body + instant head + head-leading: head responds immediately
  to mouse, body lags via look_at_speed=180.

This is an experiment. If procedural feels worse, revert by re-enabling
walk.anim + idle_lower.anim + locomotion-block.

rigs/humanoid.rig.json

@@ -4,7 +4,7 @@
   "bones": [
     { "id": "root",        "parent": null,         "rest": {"x":   0, "y":   0, "rot": 0},                   "z_order": -1 },
     { "id": "body",        "parent": "root",       "rest": {"x":   0, "y":   0, "rot": 0},                   "z_order":  2, "texture": "body_001", "look_at": true, "look_at_speed": 180 },
-    { "id": "head",        "parent": "body",       "rest": {"x":   0, "y":  -3, "rot": 0, "rot_min": -90, "rot_max": 90}, "z_order":  6, "texture": "head_001", "look_at": true, "look_at_speed": 480 },
+    { "id": "head",        "parent": "body",       "rest": {"x":   0, "y":  -3, "rot": 0, "rot_min": -90, "rot_max": 90}, "z_order":  6, "texture": "head_001", "look_at": true },
     { "id": "shoulders",   "parent": "body",       "rest": {"x":   0, "y":   0, "rot": 0},                   "z_order":  5, "texture": "shoulder_001" },
     { "id": "upper_arm_l", "parent": "shoulders",  "rest": {"x": -19, "y":  -3, "rot": 0, "scl": [-1,  1]}, "z_order":  3, "texture": "upper_arm_001" },
     { "id": "upper_arm_r", "parent": "shoulders",  "rest": {"x":  20, "y":  -4, "rot": 0},                   "z_order":  3, "texture": "upper_arm_001" },
@@ -18,19 +18,5 @@
   "tracks": [
     { "id": "lower", "bones": ["leg_l", "leg_r", "foot_l", "foot_r"] },
     { "id": "upper", "bones": ["body", "head", "shoulders", "upper_arm_l", "upper_arm_r", "lower_arm_l", "lower_arm_r"] }
-  ],
-  "locomotion": {
-    "mode": "procedural",
-    "step_trigger":        [6,  24],
-    "step_placement":      [16, 28],
-    "step_duration":       0.18,
-    "step_height":         0,
-    "idle_return_delay":   0.5,
-    "idle_return_stagger": 0.3,
-    "idle_step_duration":  0.25,
-    "legs": [
-      { "leg": "leg_l", "foot": "foot_l", "group": 0 },
-      { "leg": "leg_r", "foot": "foot_r", "group": 1 }
-    ]
-  }
+  ]
 }