feat(security): Security Center — firewall, NAT, bandwidth, posture, connections (v0.14.0-beta)

A dedicated top-level Security section plus a Meraki/UniFi-grade firewall built
on the full RouterOS feature set.

Security Center (new /security page)
- Fleet hardening scores, per-device posture list, and a "Common Findings"
  rollup aggregating identical issues across the fleet
- "Manage" deep-links into the device's Security tab (?tab= support added)

Firewall & NAT (per device + in Security Center)
- Friendly rule builder: Allow/Drop/Reject chips, Any/Address/Address-List
  pickers, port presets, connection-state chips, logging, live plain-English
  preview
- Address lists as reusable objects, referenced from rules
- Rule reordering (/ip/firewall/{filter,nat}/move); per-rule hit counters
  (print stats) with dead-rule highlighting + reset
- NAT wizards: Port Forward / Masquerade / 1:1 NAT + Custom
- Safe-apply lockout guard: backend 409 on an unscoped input drop/reject that
  would sever management; UI confirms before forcing (detectLockoutRisk, tested)

Access & security
- Security posture audit: graduated, de-duplicated scoring that never proposes
  disabling the management service the platform connects through (no self-
  lockout); switch-aware input-firewall severity; service hardening table
- Bandwidth: simple-queue CRUD + one-click "Limit this client" on client detail
- Active connections viewer

These L3 features are available on all managed RouterOS devices (routers,
switches, APs), not gated by device type.

Backend: DeviceCollector address-list/move/stats/connections/queues/service
methods; device routes for all of the above; firewallSafety + firewallSummary
utils with unit tests (19 new).

Security: bump nodemailer 8 -> 9.0.1 to clear GHSA-p6gq-j5cr-w38f (our
createTransport/sendMail usage is unaffected by the advisory's raw-option path).

Verified live against RouterOS devices; lint/typecheck/build/jest green in both
workspaces; npm audit --audit-level=high clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/layout/Sidebar.tsx

@@ -15,6 +15,7 @@ const navItems = [
   { to: '/devices',   icon: Router,          label: 'Devices' },
   { to: '/clients',   icon: Users,           label: 'Clients' },
   { to: '/traffic',   icon: Activity,        label: 'Traffic' },
+  { to: '/security',  icon: Shield,          label: 'Security' },
   { to: '/events',    icon: Bell,            label: 'Events' },
   { to: '/topology',  icon: GitBranch,       label: 'Topology' },
   { to: '/backups',   icon: HardDrive,       label: 'Backups' },