Implement M6: functional GUI views, GitHub Actions CI

Wire all remaining dashboard views to real API: agent detail page
with heartbeat status and capabilities, audit trail with time range/
actor/resource filters, notifications with grouped-by-cert view and
read/unread state, policies with severity summary bar, new issuers
and targets list views. Add GitHub Actions CI with parallel Go and
Frontend jobs. Update Makefile with test-cover and frontend-build
targets.

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

web/src/components/Layout.tsx

@@ -7,6 +7,8 @@ const nav = [
   { to: '/jobs',          label: 'Jobs',          icon: 'M4 4v5h.582m15.356 2A8.001 8.001 0 004.582 9m0 0H9m11 11v-5h-.581m0 0a8.003 8.003 0 01-15.357-2m15.357 2H15' },
   { to: '/notifications', label: 'Notifications', icon: 'M15 17h5l-1.405-1.405A2.032 2.032 0 0118 14.158V11a6.002 6.002 0 00-4-5.659V5a2 2 0 10-4 0v.341C7.67 6.165 6 8.388 6 11v3.159c0 .538-.214 1.055-.595 1.436L4 17h5m6 0v1a3 3 0 11-6 0v-1m6 0H9' },
   { to: '/policies',      label: 'Policies',      icon: 'M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-6 9l2 2 4-4' },
+  { to: '/issuers',       label: 'Issuers',       icon: 'M15 7a2 2 0 012 2m4 0a6 6 0 01-7.743 5.743L11 17H9v2H7v2H4a1 1 0 01-1-1v-2.586a1 1 0 01.293-.707l5.964-5.964A6 6 0 1121 9z' },
+  { to: '/targets',       label: 'Targets',       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' },
   { to: '/audit',         label: 'Audit Trail',   icon: 'M12 8v4l3 3m6-3a9 9 0 11-18 0 9 9 0 0118 0z' },
 ];