Add movement accel/decel, camera smoothing, and Running animator hook

- Smooth acceleration/deceleration on ground and air movement
- Interpolated scroll zoom and low-pass smoothed orbit rotation
- Drive Animator "Running" bool while moving on the ground
- Add Paintman animator controllers and animation clips
- Update README and GAME_DESIGN docs for sprint, accel, camera smoothing and animator hookup

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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