[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.

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