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)

tests/test_api.py

@@ -462,7 +462,7 @@ class TestProxyDomains:
         mock_post.return_value = {"domain": "ex.com"}
         resp = client.post(
             "/api/proxy/domains",
-            json={"domain": "ex.com", "backend_host": "10.0.0.1", "backend_port": 80},
+            json={"domain": "ex.com", "backend": "webui"},
         )
         assert resp.status_code == 200