refactor: Split FFmpeg manager into modular components

- Created ffmpeg package with specialized modules
- Improved Docker compatibility using /tmp
- Better permission handling
- More robust error handling
- Separated concerns for easier maintenance
- Simplified imports through __init__.py

videoarchiver/ffmpeg/exceptions.py

@@ -0,0 +1,13 @@
+"""FFmpeg-related exceptions"""
+
+class FFmpegError(Exception):
+    """Base exception for FFmpeg-related errors"""
+    pass
+
+class GPUError(FFmpegError):
+    """Raised when GPU operations fail"""
+    pass
+
+class DownloadError(FFmpegError):
+    """Raised when FFmpeg download fails"""
+    pass