Refactor ACME module and add cert issuance conflict handling

- Move acme.sh utilities (_run_acme, _find_acme, etc.) from lib/state to lib/acme
- Rewrite _parse_list_output to support pipe, tab, and column-separated formats
- Add ConflictError (409) to block issuing when cert already exists
- Move _find_issuance helper to detect in-progress issuance per domain
- Update issue_cert to check existing certs and return issuance status
- Fix start_polling to accept event loop explicitly
- Add sudoers entry for chown on vacuum-wall.conf
- Extend systemd ReadWritePaths for /run/nginx.pid and /var/log/nginx
- Update frontend to handle 'existing' issuance status

system/systemd/vacuum-walld.service

@@ -19,7 +19,7 @@ Environment=HOME={{ PROJECT_DIR }}
 
 # Security hardening
 ProtectSystem=strict
-ReadWritePaths={{ PROJECT_DIR }} /tmp /etc/systemd/network /etc/nginx /etc/dnsmasq.d /etc/wireguard /run/sudo /run/firewalld /run/nginx
+ReadWritePaths={{ PROJECT_DIR }} /tmp /etc/systemd/network /etc/nginx /etc/dnsmasq.d /etc/wireguard /run/sudo /run/firewalld /run/nginx /run/nginx.pid /var/log/nginx
 PrivateTmp=yes
 ProtectKernelTunables=yes
 ProtectKernelModules=yes