Add trace hotspot insights

[rogierx]

Summary

• add a trace hotspot summarizer that ranks loaded trace nodes by duration and type count
• expose hotspot rows in the webview through a typed traceInsights message
• let selecting a hotspot filter the tree to that node and jump to the source span when available
• remove package-manager caching from the tag-triggered release workflow

Fixes #42.

Validation

• pnpm exec vitest run test/index.test.ts
• pnpm run typecheck
• pnpm exec eslint src/traceAnalysis.ts src/traceTree.ts src/handleMessages.ts shared/src/messages.ts ui/src/appState.ts ui/app.vue test/index.test.ts
• pnpm exec nuxt build ui
• pnpm exec rollup -c
• git diff --check