feat(reframe): add AI-powered smart reframe for auto-cropping landscape to portrait

- Add new reframe.py module with face detection and tracking using Haar cascades
- Implement three-phase pipeline: analyze faces across sampled frames, smooth positions with interpolation and exponential moving average, render cropped output
- Support target aspect ratios: 9:16 (TikTok/Reels/Shorts), 1:1 (Square), 4:5 (Instagram Portrait)
- Add interactive CLI for reframe configuration with customizable face detection parameters
- Preserve original audio track in output video
- Include progress indicators for analysis and rendering phases
- Automatically handle even-number rounding for encoder compatibility
- Integrate with existing validation and FFmpeg utilities

Author: hariharen9