[Bug]: Composer cache directory is created in project root and not gitignored

[kanevbg]

Expected behavior

The default skeleton setup should not leave Composer runtime/cache artifacts as untracked project files.

Either /cache/ should be included in the default .gitignore, or the default Docker Composer configuration should use a Composer home/cache path outside the project root.

With the current docker-compose.yaml setting COMPOSER_HOME=/var/www/html, the expected behavior is that the resulting /cache/ directory is ignored by Git by default.

Actual behavior

pimcore/skeleton v2026.1.2 sets COMPOSER_HOME to /var/www/html in docker-compose.yaml.

Because of that, when Composer is run inside the php container, Composer uses /var/www/html/cache as its default cache directory. Since /var/www/html is the project root mount, this creates a project-root /cache directory.

The generated /cache directory is not ignored by the skeleton .gitignore, so it appears as an untracked Git directory.

Steps to reproduce

1. Create a new project from pimcore/skeleton v2026.1.2:
   composer create-project pimcore/skeleton --no-scripts my-project

2. Go to the project:
   cd my-project

3. Start the default Docker setup:
   docker compose up -d

4. Run Composer inside the php container:
   docker compose exec -T php composer install

5. Verify Composer's cache configuration:
   docker compose exec -T php composer config --list --source | grep -E 'home|cache-dir'

6. Initialize Git, because a new create-project checkout is not necessarily a Git repository:
   git init

7. Check Git status:
   git status --short

8. Observe that /cache is created in the project root and appears as untracked.

The Git initialization step is only used to demonstrate that the generated /cache directory is not ignored by the default .gitignore.