chore: remove unused desktop app, cloud deployment infra, and monitoring stack

Deletes desktop/ (Electron wrapper), deployments/ (Helm/Kustomize/
Terraform/CI for cloud deploy), and monitoring/ (Prometheus + Grafana
stack) along with DESKTOP.md, DEPLOYMENT.md, docker-compose.full.yml,
their npm scripts, and every dangling reference across README,
ARCHITECTURE, INSTALL, SETUP, docs/, and the repeated per-file
MODULE_GUIDE "Observability" boilerplate comment. The GET /api/metrics
endpoint itself is untouched — it's the dashboard's own route, not
part of the removed monitoring stack.

server/routes/metrics.js

@@ -17,8 +17,7 @@
  * server as anything other than loopback (e.g. Prometheus in Docker via
  * `host.docker.internal`) must therefore be allowlisted with
  * `DASHBOARD_ALLOWED_HOSTS` (and send the token when one is set), so an instance
- * never leaks operational data to an unexpected origin. The turnkey Prometheus +
- * Grafana bundle in `monitoring/` documents the exact setup.
+ * never leaks operational data to an unexpected origin.
  *
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */