fix: prevent duplicate nginx location block for Laravel apps

[fzengin19]

Fixes #7867

When deploying Laravel applications with Nixpacks, the nginx configuration was failing with 'duplicate location "/"' error.

Root cause:

• Nixpacks nginx template has two conditional 'location /' blocks:
  1. When IS_LARAVEL=true (detected automatically for Laravel apps)
  2. When NIXPACKS_PHP_FALLBACK_PATH is set
• Coolify was setting NIXPACKS_PHP_FALLBACK_PATH for Laravel apps, causing both conditions to be true and creating duplicate blocks.

Solution:

• Remove NIXPACKS_PHP_FALLBACK_PATH for Laravel apps since IS_LARAVEL=true already configures the correct nginx routing.
• Keep NIXPACKS_PHP_ROOT_DIR to ensure proper public directory configuration.

Tested with TALL stack (Tailwind, Alpine, Livewire, Laravel) project containing both composer.json and package.json - nginx now starts correctly.