[Bug] Worktree creation generates broken Nginx config for Herd

## Description

When Polyscope creates a worktree, it appears to register a new site in Laravel Herd's Nginx configuration. However, the generated config file contains empty replacement strings, which causes Nginx to fail to start entirely.

## Version

- Polyscope: **0.14.0**
- Laravel Herd (macOS)

## Steps to reproduce

1. Use Polyscope to create a worktree (e.g. for a PR)
2. Herd's Nginx server crashes and fails to restart

## Root cause

The generated Nginx site config (in `~/Library/Application Support/Herd/config/valet/Nginx/`) contains empty strings where paths should be:

```nginx
location / {
rewrite ^ "" last; # ← empty replacement, invalid in Nginx
}

error_page 404 ""; # ← empty
fastcgi_index ""; # ← empty
fastcgi_param SCRIPT_FILENAME ""; # ← empty
```

Nginx throws:
```
[emerg] empty replacement in .../config/valet/Nginx/jolly-newt.test:28
nginx: configuration file ... test failed
```

This prevents **all** Herd sites from working, not just the Polyscope worktree site.

## Expected behavior

The generated Nginx config should contain valid paths pointing to the worktree directory, or the site should not be registered in Herd if the paths are unavailable.

## Workaround

Manually delete the broken config file from `~/Library/Application Support/Herd/config/valet/Nginx/` and restart Herd.

Start by reproducing worktree creation for a PR and inspect the generated file in ~/Library/Application Support/Herd/config/valet/Nginx/. Trace the worktree-to-Herd registration entry point and determine why the rewrite, error_page, fastcgi_index, and SCRIPT_FILENAME values are empty. Done means the generated site has valid worktree paths, or is not registered when paths are unavailable, and Herd's Nginx configuration starts successfully.

Rédigé par le modèle d'indexation à partir du texte de l'issue.