[codex] Release GuitarToolkit v1.8.0 with Melody Transformer

[LuTiK1984]

Summary / Кратко

• adds the complete Melody Transformer runtime workflow and editable Melody sketchbook
• expands ML Trainer with v2/v3 datasets, evaluation, preview, evolution, ONNX export, and model installation
• improves melody synthesis, playback safety, phrase controls, octave/interval behavior, and compact layout
• packages Transformer v2/v3 tools and vocabularies in the ML Trainer release archive
• prepares version 1.8.0, changelog, README, release docs, checksums, and optional Authenticode signing

Verification / Проверка

• dotnet restore GuitarToolkit.sln
• dotnet build GuitarToolkit.sln --no-restore --configuration Debug --verbosity minimal — 0 warnings, 0 errors
• dotnet test GuitarToolkit.sln --no-restore --configuration Debug --verbosity minimal — 78/78 passed
• Python py_compile for all Melody Transformer scripts
• build-release.ps1 -Version 1.8.0 -Configuration Release
• Desktop, VST3, and ML Trainer archives plus SHA-256 files generated
• Final manual Desktop smoke test
• Final manual VST3/DAW smoke test

Checklist / Чеклист

• Change is focused on the Melody Transformer and v1.8.0 release
• CHANGELOG.md updated
• README and release documentation updated
• GuitarToolkit.Core remains independent from WPF, NAudio, and AudioPlugSharp
• UI prototype work is intentionally excluded from this PR

DAW Notes / Заметки по DAW

No audio callback or VST processing changes were made. Final host smoke testing is still recommended before publishing the release.