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/db_user_password.txt.example

@@ -0,0 +1,8 @@
+# Database User Password Example
+# Copy this file to db_user_password.txt and set your local development password
+# Example: local-dev-db-password-2024
+#
+# Generate secure password:
+# openssl rand -base64 32
+#
+# Note: This password should match DB_PASSWORD in your .env.local (if you still use it during migration)