Plugin installation fail behind corporate firewall

### Expected Behavior

There would be an option to configure which registry `yarn` talks to instead of hard-coded `registry.npmjs.org`

### Actual Behavior

All operations accessing `registry.npmjs.org` fail.

### Reproduction Steps

_No response_

### Is there an existing issue for this?

- [x] I have searched the [issue tracker](https://www.github.com/Kong/insomnia/issues) for this problem.

### Which sync method do you use?

- [ ] Git sync.
- [x] Insomnia Cloud sync.
- [x] Local only

### Additional Information

_No response_

### Insomnia Version

v11.6.1

### What operating system are you using?

macOS

### Operating System Version

26.0.1 (25A362)

### Installation method

Homebrew

### Last Known Working Insomnia version

_No response_

The issue does not name any files or tests; start by locating the plugin installation path and its use of the hard-coded registry.npmjs.org value. Done means users can configure the Yarn registry and plugin installation succeeds behind a corporate firewall.

Written by the indexing model from the issue text.