chore: initial skeleton

- docs/architecture.md: native rewrite plan (5 services + control plane,
  Active-Active cluster like nmg, Floating-IP for HTTP ingress)
- cmd/edgeguard-{api,scheduler,ctl}: minimal Gin + CLI stubs
- packaging/debian/edgeguard-{api,ui,meta}: control + maintainer scripts
- deploy/systemd/edgeguard-api.service + edgeguard-scheduler.service
  with hardening defaults
- Makefile: build / cross-compile (amd64+arm64) / deb / publish targets
- scripts/install.sh + scripts/apt-repo/build-package.sh stubs

packaging/debian/edgeguard-api/DEBIAN/prerm

@@ -0,0 +1,21 @@
+#!/bin/bash
+set -e
+
+case "$1" in
+    remove|upgrade|deconfigure)
+        systemctl stop edgeguard-api.service edgeguard-scheduler.service || true
+        systemctl disable edgeguard-api.service edgeguard-scheduler.service || true
+        ;;
+
+    failed-upgrade)
+        ;;
+
+    *)
+        echo "prerm called with unknown argument \`$1'" >&2
+        exit 1
+        ;;
+esac
+
+#DEBHELPER#
+
+exit 0