Add a Running exercise with an animated stride figure

Stance and flight keyframes with single-frame foot pins for the strikes,
forward lean, opposite-arm drive, and daylight under both feet in flight —
distinct from Cardio's high-knee march, which stays as is.

Claude-Session: https://claude.ai/code/session_01PKptrgbx74peTwHGRxBojv

Exercise Library/Running/info.md

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+# Running
+
+Steady, easy-pace running — an upright posture with a slight forward lean from
+the ankles, a light midfoot landing under the hips, and a relaxed, efficient
+stride. Run in place, on a treadmill, or outdoors; your Apple Watch records
+the real effort — heart rate, calories, and duration — as a running workout.
+
+- **Category:** Cardio
+- **Type:** Aerobic / conditioning
+- **Targets:** Heart, lungs, legs, endurance
+- **Prescription:** 15–30 minutes at a conversational-to-brisk pace
+- **Defaults:** 1 × 1200 s
+
+## Setup
+
+Stand tall with a slight forward lean from the ankles, not the waist. Let
+your watch start the session so the effort is tracked on your wrist.
+
+## Execution
+
+1. Ease in for the first minute or two, letting your heart rate climb.
+2. Land lightly on your midfoot, under your hips — not out in front.
+3. Drive your knees forward and let your arms swing opposite your legs.
+4. Favor a quicker cadence over a longer stride; settle into a pace you can
+   hold for the whole block.
+5. Cool down with an easy minute before you stop.
+
+## Cues
+
+- Keep your posture tall, with the lean coming from the ankles.
+- Relax your shoulders and keep your elbows around 90 degrees.
+- Aim for a pace where you could speak in short sentences, not full paragraphs.
+
+## Common Mistakes
+
+- Overstriding — reaching the foot out ahead of the hips on landing.
+- Starting too hard and fading long before the time is up.
+- Hunching forward at the waist instead of leaning from the ankles.
+
+## Progression
+
+Add minutes, lift the pace, or fold in short faster intervals to raise the
+challenge over time.