Update changelog: fix WhisperX installation, dependency pins, and GPU…

[chris-colinsky]

… setup steps

Summary

Pre-release validation exposed three dependency issues that prevented WhisperX from loading in a clean venv. All are fixed; a full venv teardown and rebuild now works end-to-end with make dev-setup.

Changes

• Pin WhisperX install to commit 741ab9a (v3.7.6) — the v3.1.1 tag uses an older API without the device_index parameter required by the ctranslate2 backend
• Expand make install-whisperx to also install WhisperX runtime deps (av, ctranslate2, faster-whisper, flatbuffers, nltk, onnxruntime) omitted by --no-deps
• Cap transformers at <4.40.0 — 4.40+ requires a PyTorch 2.2 pytree API that breaks with the pinned PyTorch 2.1.2
• Add make install-torch-cuda and run it as the final step of make dev-setup — uv sync silently replaces CUDA wheels with CPU-only builds from PyPI
• Update README installation steps to use make dev-setup as a single command and correct the post-install verification steps
• Update CHANGELOG with correct release date and document all four fixes under [0.1.0]

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing behavior to change)
• Documentation update

Testing

• Unit tests pass: make test
• All checks pass: make all-checks
• New tests added for new functionality
• Integration tests verified (if applicable — requires GPU)

Checklist

• Code follows the project style (ruff lint + format clean)
• CHANGELOG.md updated under [Unreleased]
• Documentation updated if CLI options or behavior changed
• No new dependency pins added without explanation

Related Issues

Closes #