feat: improve output-path handling and error messages

- If --output-path is a directory, output file uses default naming in that directory
- If --output-path is a file, use as-is
- Improved directory existence/writability checks and error messages
- Updated CLI help and documentation to describe new behavior
- Cleaned up unused imports and resolved all warnings
- Ensured ffmpeg failures are clearly reported to the user

.idea/.gitignore

@@ -0,0 +1,8 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml