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)

lib/system_import.py

@@ -840,7 +840,7 @@ def import_firewall() -> bool:
         return False
 
     try:
-        output = run("firewall-cmd --list-all-zones", sudo=True)
+        output = run(["firewall-cmd", "--list-all-zones"], sudo=True)
     except RuntimeError:
         logger.warning("Import failed for firewall: firewall-cmd unavailable")
         return False