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/Hip Thrust/info.md

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+# Hip Thrust
+
+The loaded glute bridge — shoulders on a bench, barbell across the hips,
+drive the hips up to a straight line.
+
+- **Category:** Main circuit
+- **Type:** Free-weight hip extension
+- **Targets:** Glutes, hamstrings
+- **Prescription:** 4 × 8–10
+
+## Setup
+
+Sit on the floor with your upper back against a bench, the bar (padded)
+across your hips, hands steadying it. Feet flat, hip-width, heels under
+the knees.
+
+## Execution
+
+1. Brace, tuck the chin, and drive through the heels to lift the hips.
+2. Stop when shoulders, hips and knees are level — a flat tabletop.
+3. Squeeze the glutes at the top, then lower the hips under control.
+
+## Cues
+
+- Chin tucked, ribs down — the body hinges around the bench edge.
+- Full lockout comes from the glutes, not from arching the back.
+- Shins vertical at the top; adjust foot distance until they are.
+
+## Common Mistakes
+
+- Overarching the lower back instead of finishing with the glutes.
+- Feet too far forward, turning it into a hamstring exercise.
+- Cutting the range short at the top.
+
+## Progression
+
+Start with the bar alone to groove the pattern, then add plates; pause
+reps at the top for extra glute work.