feat(M48): continuous TLS health monitoring — endpoint state machine, shared tlsprobe, 8 API endpoints, GUI

Adds continuous TLS endpoint health monitoring that closes the deploy→verify→monitor loop.
After M25 verifies a deployment succeeded once, M48 continuously confirms it stays healthy.

Key components:
- Shared `internal/tlsprobe/` package extracted from network scanner for reuse
- Health status state machine: healthy → degraded (2 failures) → down (5 failures),
  plus cert_mismatch when served fingerprint differs from expected
- 8th scheduler loop (60s tick, per-endpoint configurable intervals)
- PostgreSQL migration 000011: endpoint_health_checks + endpoint_health_history tables
- 8 REST API endpoints (CRUD, history, acknowledge, summary)
- Health Monitor GUI page with summary bar, status table, create modal, auto-refresh
- 38 new tests (5 tlsprobe + 11 domain + 10 service + 8 handler + 4 frontend)
- All coverage thresholds maintained (service 68%, handler 83%, domain 87%, middleware 63%)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/components/Layout.tsx

@@ -18,6 +18,7 @@ const nav = [
   { to: '/agent-groups',  label: 'Agent Groups',  icon: 'M19 11H5m14 0a2 2 0 012 2v6a2 2 0 01-2 2H5a2 2 0 01-2-2v-6a2 2 0 012-2m14 0V9a2 2 0 00-2-2M5 11V9a2 2 0 012-2m0 0V5a2 2 0 012-2h6a2 2 0 012 2v2M7 7h10 M9 3v2m6-2v2' },
   { to: '/discovery',     label: 'Discovery',       icon: 'M21 21l-6-6m2-5a7 7 0 11-14 0 7 7 0 0114 0z' },
   { to: '/network-scans', label: 'Network Scans',  icon: 'M3.055 11H5a2 2 0 012 2v1a2 2 0 002 2 2 2 0 012 2v2.945M8 3.935V5.5A2.5 2.5 0 0010.5 8h.5a2 2 0 012 2 2 2 0 104 0 2 2 0 012-2h1.064M15 20.488V18a2 2 0 012-2h3.064M21 12a9 9 0 11-18 0 9 9 0 0118 0z M9 12l2 2 4-4' },
+  { to: '/health-monitor', label: 'Health Monitor', icon: 'M4.318 6.318a4.5 4.5 0 000 6.364L12 20.364l7.682-7.682a4.5 4.5 0 00-6.364-6.364L12 7.636l-1.318-1.318a4.5 4.5 0 00-6.364 0z' },
   { to: '/short-lived',   label: 'Short-Lived',    icon: 'M13 10V3L4 14h7v7l9-11h-7z' },
   { to: '/digest',        label: 'Digest',         icon: 'M3 8l7.89 5.26a2 2 0 002.22 0L21 8M5 19h14a2 2 0 002-2V7a2 2 0 00-2-2H5a2 2 0 00-2 2v10a2 2 0 002 2z' },
   { to: '/observability', label: 'Observability',  icon: 'M9 19v-6a2 2 0 00-2-2H5a2 2 0 00-2 2v6a2 2 0 002 2h2a2 2 0 002-2zm0 0V9a2 2 0 012-2h2a2 2 0 012 2v10m-6 0a2 2 0 002 2h2a2 2 0 002-2m0 0V5a2 2 0 012-2h2a2 2 0 012 2v14a2 2 0 01-2 2h-2a2 2 0 01-2-2z' },

web/src/components/StatusBadge.tsx

@@ -31,6 +31,12 @@ const statusStyles: Record<string, string> = {
   pending:             'badge-warning',
   failed:              'badge-danger',
   read:                'badge-neutral',
+  // Health check statuses
+  healthy:             'badge-success',
+  degraded:            'badge-warning',
+  down:                'badge-danger',
+  cert_mismatch:       'badge-warning',
+  unknown:             'badge-neutral',
 };
 
 export default function StatusBadge({ status }: { status: string }) {