Add knip check for dependencies

[olliethedev]

Summary

Add Knip with --strict mode to detect unused dependencies, exports, and files in the @btst/stack package.

Motivation

The @btst/stack package has a large dependency tree with many peer dependencies. A strict Knip check would help:

• Identify unused dependencies and peerDependencies
• Find dead code and unused exports
• Keep the bundle size minimal
• Catch regressions in CI

Tasks

• Add knip as a dev dependency in packages/better-stack
• Create knip.json config (handle multiple entry points in exports)
• Add "knip": "knip --strict" script to packages/better-stack/package.json
• Add to root lint or create dedicated pnpm knip task
• Add to CI workflow (.github/workflows/)

Notes

May need to configure Knip's entry and ignore patterns to handle:

• Multiple plugin entry points (plugins/*/api, plugins/*/client, etc.)
• CSS exports
• typesVersions mappings