The process.env access was outside the typeof process check, which
would throw in browser environments. Moved inside the Node.js/Bun
block for consistency with other env var access.
Also added changelog entry for #1320 and improved docs clarity.
collectAutoExtensionEntries now checks if the directory itself has a
package.json with pi.extensions (or index.ts) before scanning children.
This fixes duplicate extension loading when a manifest-aware directory
is specified directly in settings.json extensions array.
Fixes#1274