Add the hinge pattern: Deadlift, RDL, Glute Bridge, Hip Thrust, Back Extension

The biggest hole in the coverage matrix - the hinge had zero entries in
any modality. Deadlift and Romanian Deadlift are the library's first
standing (camera.zoom) and first barbell motions.

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

Exercise Library/Glute Bridge/motion.json

@@ -0,0 +1,29 @@
+{
+  "name": "Glute Bridge",
+  "primary": 2,
+  "working": ["leg_r", "leg_l"],
+  "frames": [
+    {
+      "hold": 0.4, "tween": 0.8,
+      "root": {"pos": [168, 144], "pitch": -90},
+      "spine": [0, 0],
+      "neck": 20, "head": -6,
+      "shoulder_r": -4, "elbow_r": 0,
+      "shoulder_l": -4, "elbow_l": 0,
+      "hip_r": 72, "knee_r": 82, "ankle_r": 5,
+      "hip_l": 72, "knee_l": 82, "ankle_l": 5,
+      "pins": {"foot_r": [205, 148], "foot_l": [209, 150]}
+    },
+    {
+      "hold": 0.9, "tween": 1.0,
+      "root": {"pos": [172, 116], "pitch": -110},
+      "spine": [0, -4],
+      "neck": 48, "head": -6,
+      "shoulder_r": -14, "elbow_r": 0,
+      "shoulder_l": -14, "elbow_l": 0,
+      "hip_r": 16, "knee_r": 92, "ankle_r": 5,
+      "hip_l": 16, "knee_l": 92, "ankle_l": 5,
+      "pins": {"foot_r": [205, 148], "foot_l": [209, 150]}
+    }
+  ]
+}