Add reproducer for coolify#8953: .env not found with preserve repository (#65)

Minimal Docker Compose example that triggers the deployment failure when
Preserve Repository is enabled with a custom start command containing
variable interpolation.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

docker-compose-preserve-repo-env/README.md

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+# Reproducer for coolify#8953
+
+Minimal Docker Compose app that uses `${WEB_PORT}` variable interpolation to
+reproduce the `.env not found` error when **Preserve Repository** is enabled
+with a custom start command.
+
+## Steps to reproduce
+
+1. In Coolify, create a **Docker Compose** application pointing to this
+   repository subdirectory (`docker-compose-preserve-repo-env`).
+2. Add an environment variable: `WEB_PORT=9090`.
+3. In **Advanced** settings, enable **Preserve Repository**.
+4. Set the custom start command to:
+   ```
+   docker compose -f docker-compose.yaml -f docker-compose.prod.yaml up -d
+   ```
+5. Deploy.
+
+### Expected (after fix)
+
+Deployment succeeds. `--project-directory` in the `up -d` command points to
+`/data/coolify/applications/{uuid}` (host path where `.env` exists).
+
+### Actual (before fix)
+
+Deployment fails with:
+
+```
+env file /artifacts/{deployment_uuid}/.env not found
+```
+
+Because `--project-directory` was set to `/artifacts/{deployment_uuid}` (helper
+container path), and Docker Compose resolves `env_file` directives relative to
+that directory.
+
+## Related
+
+- https://github.com/coollabsio/coolify/issues/8953

docker-compose-preserve-repo-env/docker-compose.prod.yaml

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+services:
+  web:
+    restart: always

docker-compose-preserve-repo-env/docker-compose.yaml

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+services:
+  web:
+    image: nginx:alpine
+    ports:
+      - "${WEB_PORT:-8080}:80"