Replace the previous whisper.cpp-based word alignment with a fully ONNX-based
implementation using onnxruntime-node and @huggingface/tokenizers. Add new
Whisper ONNX model management, alignment mapping, and spectral analysis modules.
Remove all code and documentation referencing whisper.cpp, update environment
variables, Dockerfile, and docs to reflect ONNX-only alignment. Add unit tests
for alignment and ONNX model logic.
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