fix(art): replace stick-figure athlete with the BetterFit mark

[johnnyhuy]

Summary

The workout card hero drew a single-stroke stick figure with a red bar through it for the push pose. That read as clip art and fights the design system's rule that illustration must use heavy geometric forms with the same high-contrast confidence as the mark.

AthleteIllustration now renders three compressed white ovals on an ember-tinted surface — the same three-oval form BetterFit's brand mark uses for plates / repetition / forward momentum — with a small SF Symbol (arrow.up / arrow.down / figure.walk / heart.fill) offset below the mark as a category hint.

• Removed: gradientColors, segments(), point(), drawAthlete(), categoryColor
• Removed AthletePose.compound and .all cases (unused, kept the four real categories)
• Card hero space on PlayingCardWorkoutCard grows from 100x140 to 140x140 so the mark has room to breathe
• AthleteIllustration.size is now an explicit parameter (default 140)

Consequences

• Same three-oval brand mark used for the mascot and the workout card hero — visual coherence across identity moments and product surfaces
• The mark stays on the ember product accent (per spec: yellow is for brand moments only, the card hero is product UI)
• No behavioural change; the card still surfaces the workout name, duration, equipment, and category badge as primary information

Testing

• 95 SwiftPM tests pass
• iOS build clean
• Visual: workout card reads as the same brand mark as the greeting, no stick figure
• Targeted UI test passes

Co-authored-by: opencode-agent noreply@opencode.ai