fix: critical bugs + security hardening

Phase 1 (critical bugs):
- Fix firewall import string-to-list bug (system_import.py)
- Add rich rules removal in firewall config apply (handlers/firewall.py)

Phase 2 (security hardening):
- Restrict sudo wildcards to specific paths (sudoers.d/vacuum-walld)
- Fix TOCTOU: use /run/vacuum-wall/ for temp files (nginx, dnsmasq, network handlers)
- Remove unnecessary sudo from wg genkey/pubkey (handlers/wireguard.py)

Phase 3 (validation):
- Validate poll intervals > 0 (daemon/server.py)
- Restrict sysctl to whitelisted parameters (handlers/network.py)

Phase 4 (defensive programming):
- Enforce shell=False in run() and run_proc() (lib/common.py)
- Track issuance tasks for graceful shutdown (handlers/acme.py)
- Add nginx template marker consistency tests (tests/test_system_import.py)

system/systemd/vacuum-walld.service

@@ -18,9 +18,13 @@ Environment=PYTHONUNBUFFERED=1
 Environment=ACME_HOME={{ PROJECT_DIR }}/data/acme
 Environment=HOME={{ PROJECT_DIR }}
 
+# Runtime directory for temp files used during config apply
+RuntimeDirectory=vacuum-wall
+RuntimeDirectoryMode=0750
+
 # Security hardening
 ProtectSystem=strict
-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
+ReadWritePaths={{ PROJECT_DIR }} /tmp /etc/systemd/network /etc/nginx /etc/dnsmasq.d /etc/wireguard /run/vacuum-wall /run/sudo /run/firewalld /run/nginx /run/nginx.pid /var/log/nginx
 PrivateTmp=yes
 ProtectKernelTunables=yes
 ProtectKernelModules=yes