fix(erpnext): run bench setup production as root, add nginx+supervisor

- bench setup production requires root (is_root check) - was failing as frappe user
- Add nginx and supervisor as apt dependencies for production setup
- Remove custom erpnext.service - bench manages gunicorn+workers via supervisor
- Port 8000 → 80 (nginx reverse proxy)
- Fix bench update in CT to run as frappe user with proper PATH

json/erpnext.json

@@ -8,7 +8,7 @@
     "type": "ct",
     "updateable": true,
     "privileged": false,
-    "interface_port": 8000,
+    "interface_port": 80,
     "documentation": "https://docs.erpnext.com/",
     "website": "https://erpnext.com/",
     "logo": "https://cdn.jsdelivr.net/gh/selfhst/icons@main/webp/erpnext.webp",