Add the free-weight canon and bodyweight staples (16 exercises)

Squat/lunge: Barbell Squat, Goblet Squat, Bodyweight Squat, Lunge.
Bench station: Bench Press, Incline Bench Press, Dumbbell Bench Press,
Dumbbell Fly (the fly authors the face-on camera for its frontal arc).
Dumbbell rack: Dumbbell Row, Dumbbell Shoulder Press, Dumbbell Curl,
Lateral Raise - first uses of the dumbbell prop. Bodyweight: Push-Up,
Pull-Up, Crunch, Dip.

Claude-Session: https://claude.ai/code/session_01HJDQQDA9QdP8zByg43H5v3

Exercise Library/Dip/motion.json

@@ -0,0 +1,36 @@
+{
+  "name": "Dip",
+  "primary": 2,
+  "camera": {"zoom": 0.78},
+  "working": ["arm_r", "arm_l"],
+  "props": [
+    {"type": "scene", "shapes": [
+      {"kind": "line", "pts": [[176, 66], [176, 150]], "w": 5},
+      {"kind": "circle", "c": [176, 61], "r": 3.5, "fill": true, "color": "prop"}
+    ]}
+  ],
+  "frames": [
+    {
+      "hold": 0.4, "tween": 1.1,
+      "root": {"pos": [160, 86], "pitch": 8},
+      "spine": [0, 0],
+      "neck": 5, "head": -10,
+      "shoulder_r": 2, "elbow_r": 8,
+      "shoulder_l": 2, "elbow_l": 8,
+      "hip_r": 45, "knee_r": 130, "ankle_r": -20,
+      "hip_l": 45, "knee_l": 130, "ankle_l": -20,
+      "pins": {"hand_r": [174, 60], "hand_l": [178, 62]}
+    },
+    {
+      "hold": 0.4, "tween": 1.0,
+      "root": {"pos": [160, 116], "pitch": 18},
+      "spine": [0, 4],
+      "neck": 8, "head": -15,
+      "shoulder_r": -30, "elbow_r": 110,
+      "shoulder_l": -30, "elbow_l": 110,
+      "hip_r": 78, "knee_r": 148, "ankle_r": -20,
+      "hip_l": 78, "knee_l": 148, "ankle_l": -20,
+      "pins": {"hand_r": [174, 60], "hand_l": [178, 62]}
+    }
+  ]
+}