refactor(specs): merge 08-infrastructure into canonical 04-06 dirs

- Append live QNAP configs to 04-01-docker-compose.md (Appendix A)
  - MariaDB+PMA, Redis+Elasticsearch, NPM, Gitea, n8n, App stack
- Append SSH setup + Secrets management to 04-06-security-operations.md
  - Appendix A: SSH key setup, config, hardening, port forwarding
  - Appendix B: .env structure, secret generation, rotation, GPG backup
- Append QNAP/Gitea CI/CD docs to 04-04-deployment-guide.md
  - Appendix A: Container Station deployment steps
  - Appendix B: Gitea Actions CI/CD pipeline setup
  - Appendix C: act_runner (ASUSTOR) installation
- Move Git_command.md -> 05-Engineering-Guidelines/05-05-git-cheatsheet.md
- Move docker-compose-app.yml, lcbp3-monitoring.yml, lcbp3-registry.yml,
  grafana/ -> 04-Infrastructure-OPS/
- Archive lcbp3-db.md -> 99-archives/
- Remove all legacy 08-infrastructure/* files from git
- Remove Google OAuth client_secret JSON from git index (security)
- Add .gitignore rules: *client_secret*.json, *service_account*.json,
  specs/08-infrastructure/
- Update 04-Infrastructure-OPS/README.md with new file index

.gitignore

@@ -70,6 +70,10 @@ report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json
 .env.test.local
 .env.production.local
 *.pem
+# Secrets — NEVER commit OAuth credentials or service account keys
+*client_secret*.json
+*service_account*.json
+specs/08-infrastructure/
 
 # ============================================
 # Testing & Coverage