feat: Use git submodule for private dependency

- Add wc-licensed-product-client as git submodule in lib/
- Change Composer repository from VCS to path type
- CI now checks out submodules recursively
- Remove COMPOSER_AUTH (no longer needed)

This solves the CI networking issue by fetching the
dependency via git submodule instead of Composer.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -11,6 +11,8 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
+        with:
+          submodules: recursive
 
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
@@ -30,8 +32,6 @@ jobs:
         run: composer validate --strict
 
       - name: Install Composer dependencies (production)
-        env:
-          COMPOSER_AUTH: '{"http-basic": {"src.bundespruefstelle.ch": {"username": "git", "password": "${{ secrets.SRC_GITEA_TOKEN }}"}}}'
         run: |
           composer config platform.php 8.3.0
           composer install --no-dev --optimize-autoloader --no-interaction