It's impossible to install custom plugins from outside npm
### Analysis

Years ago, I threw together this carbon dioxide sensor plugin and *somehow* installed it into Homebridge: https://github.com/SamusAranX/homebridge-http-co2

Earlier, I reimaged the rpi Homebridge was running on, making sure to download a backup archive first. When I restored this backup on a new Homebridge installation, I was greeted with the following message:
> No plugin was found for the accessory "HttpCarbonDioxide" in your config.json. Please make sure the corresponding plugin is installed correctly.

I plainly do not remember how I installed the plugin the first time because I am not a JS developer. I don't have an npm account to publish things to, nor do I want one.
The flavor text on the Backup & Restore thingy led me to believe I could just restore the backup and everything would just work, but that's obviously not true.

I've tried:
1. from the Homebridge terminal, running `npm install -g` in the project directory, which did nothing
2. copying the project folder to /var/lib/homebridge/node_modules and fixing the perms, which also did nothing

What other options do I have here?

### Expected Behavior

it just works

### Steps To Reproduce

Do what I described above

### Logs

```markdown
--
```

### Configuration

```json
--
```

### Environment

- OS: Debian 12 
- Software: Homebrige 1.9.0
- Node: v22.14.0
- npm: Whatever's bundled with this version of Homebridge


### Process Supervisor

hb-service

### Additional Context

_No response_