feat: Add comprehensive documentation suite and reorganize project structure

- Created complete documentation in docs/ directory
- Added PROJECT_OVERVIEW.md with feature highlights and getting started guide
- Added ARCHITECTURE.md with system design and technical details
- Added SECURITY.md with comprehensive security implementation guide
- Added DEVELOPMENT.md with development workflows and best practices
- Added DEPLOYMENT.md with production deployment instructions
- Added API.md with complete REST API documentation
- Added CONTRIBUTING.md with contribution guidelines
- Added CHANGELOG.md with version history and migration notes
- Reorganized all documentation files into docs/ directory for better organization
- Updated README.md with proper documentation links and quick navigation
- Enhanced project structure with professional documentation standards

deploy/ffmpeg-profiles.md

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+FFmpeg ABR Profiles (Examples)
+
+This project ships an example ABR pipeline in `deploy/abr.sh`. Below are suggested profiles and flags you can adapt.
+
+Targets (H.264 + AAC, 48 fps GOP=48):
+
+- 360p: 800 kbps (maxrate 856k, bufsize 1200k)
+- 480p: 1400 kbps (maxrate 1498k, bufsize 2100k)
+- 720p: 2800 kbps (maxrate 2996k, bufsize 4200k)
+
+Recommended flags:
+
+- Video: `-c:v libx264 -preset veryfast -g 48 -sc_threshold 0 -filter:v "scale=w=-2:h=<height>"`
+- Audio: `-c:a aac -b:a 128k -ac 2`
+- HLS: `-f hls -hls_time 4 -hls_playlist_type event -hls_flags independent_segments`
+- Var streams: `-var_stream_map 'v:0,a:0 v:1,a:1 v:2,a:2'`
+- Output pattern: `-master_pl_name master.m3u8 -hls_segment_filename /var/www/hls/abr/${ABR_STREAM_KEY}/%v/seg_%06d.ts /var/www/hls/abr/${ABR_STREAM_KEY}/%v/index.m3u8`
+
+Usage:
+
+- Set `ABR_STREAM_KEY` to the incoming RTMP stream key used by SRS.
+- Start the ABR container (already included in docker-compose) to generate `/hls/abr/<key>/{0,1,2}/index.m3u8` and `master.m3u8`.
+
+SRS-based Transcoding (Optional)
+
+SRS supports an internal `transcode` directive. If you prefer SRS to run FFmpeg for you, add a `transcode` block to `deploy/srs.conf` mapping the input app/stream to multi-rendition outputs, and write resulting HLS to the same `/srs/hls` volume.
+