feat: add stats script for filtering and analyzing emotion results

Summary

• Add stats.py script for multi-layer filtering of emotion analysis results
• Filter criteria: has_face, face_count=1, no camera movement, intensity>0.5, non-neutral
• Add analyze_stats function with progress bars and formatted output
• Support optional output file for saving filtered results

Test plan

• Run stats script on existing results JSON
• Verify filtering logic produces expected output
• Test output file generation

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