Add trace line visual tones

[rogierx]

Summary

• add VS Code theme-aware accent colors for slow, type-heavy, and mixed trace rows
• keep the tone calculation in a tested helper so thresholds are explicit
• remove package-manager caching from the tag release workflow

Fixes #40.

Validation

• pnpm run typecheck
• pnpm exec vitest run test/index.test.ts
• pnpm exec eslint src/traceTone.ts ui/components/TreeNode.vue test/index.test.ts
• pnpm exec nuxt build ui
• pnpm exec rollup -c in srcDev
• pnpm exec rollup -c