feat(local-secrets): introduce unified local secrets management and documentation

- Add example secret files for `app_key`, `db_user_password`, and `redis_password`.
- Introduce `local.vault.yml.example` for Ansible Vault encryption of local secrets.
- Create migration and setup scripts for transitioning from `.env.local` to secrets files.
- Update `docker-compose.local.yml` to adopt Docker Secrets and `_FILE` pattern for local configurations.
- Add deployment playbooks and enhanced logging configurations for local development.

secrets/app_key.txt.example

@@ -0,0 +1,8 @@
+# Application Key Example
+# Copy this file to app_key.txt and set your local development application key
+# Example: base64:local-dev-app-key-generated
+#
+# Generate application key:
+# php -r "echo 'base64:' . base64_encode(random_bytes(32));"
+#
+# Or use existing APP_KEY from .env.local