fix(package): include guide docs in npm package

[gauravsaxena1997]

Summary

• include docs/guide/ in the npm package whitelist
• keep README links such as ./docs/guide/extending-opencli.md valid for installed-package readers

Fixes #1918.

Verification

• node -e "const pkg = require('./package.json'); if (!pkg.files.includes('docs/guide/')) process.exit(1); console.log('docs/guide/ is included in package files')"
• npm pack --dry-run --json showed docs/guide/extending-opencli.md in the package file list; this worktree does not have local dev dependencies installed, so npm prepare printed missing tsx/tsc tooling during the dry run.