fix: use official Signed-By path & revert install script cleanup

- Change Signed-By from /etc/apt/keyrings/pmg.gpg to
  /usr/share/keyrings/proxmox-archive-keyring.gpg in all three
  PMG repo creation blocks (enterprise, no-subscription, test),
  matching official PMG docs and PVE post-install convention
- Remove APT source cleanup from install script (handled by
  post-pmg-install instead)

install/proxmox-mail-gateway-install.sh

@@ -22,12 +22,6 @@ setup_deb822_repo \
   "pmg-no-subscription"
 $STD apt install -y proxmox-mailgateway-container
 
-msg_info "Cleaning up duplicate APT sources"
-rm -f /etc/apt/sources.list.d/pmg-enterprise.list
-rm -f /etc/apt/sources.list.d/pmg-install-repo.list
-[[ -f /etc/apt/sources.list.d/debian.sources ]] && : >/etc/apt/sources.list
-msg_ok "Cleaned up duplicate APT sources"
-
 msg_ok "Installed Proxmox Mail Gateway"
 
 motd_ssh

tools/pve/post-pmg-install.sh

@@ -196,7 +196,7 @@ Types: deb
 URIs: https://enterprise.proxmox.com/debian/pmg
 Suites: ${VERSION}
 Components: pmg-enterprise
-Signed-By: /etc/apt/keyrings/pmg.gpg
+Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg
 EOF
       msg_ok "Added 'pmg-enterprise' repository"
       ;;
@@ -264,7 +264,7 @@ Types: deb
 URIs: http://download.proxmox.com/debian/pmg
 Suites: ${VERSION}
 Components: pmg-no-subscription
-Signed-By: /etc/apt/keyrings/pmg.gpg
+Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg
 EOF
       msg_ok "Added 'pmg-no-subscription' repository"
       ;;
@@ -291,7 +291,7 @@ Types: deb
 URIs: http://download.proxmox.com/debian/pmg
 Suites: ${VERSION}
 Components: pmgtest
-Signed-By: /etc/apt/keyrings/pmg.gpg
+Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg
 Enabled: no
 EOF
       msg_ok "Added 'pmgtest' repository"