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.

.gitignore

@@ -63,5 +63,10 @@ test-results/
 # WireGuard client configs (generated locally)
 deployment/ansible/wireguard-clients/
 
+# Local development secrets (Docker Secrets)
+secrets/*.txt
+!secrets/*.example
+deployment/ansible/secrets/local.vault.yml
+
 # SSL/TLS certificates
 **/acme.json