Add Security Center — multi-source event pipeline with dashboard UI

Introduces a unified security event store and HTTP API that ingests events
from any of the configured sources (API audit, Caddy access log, fail2ban,
shared_bans, future remote agents) and surfaces them in the dashboard.

New files:
  src/security/event-store.js      JSONL-backed store + in-memory query index
  src/security/host-registry.js    Registered hosts with per-host API keys
  src/security/event-workers.js    Tail-followers for Caddy/fail2ban/shared_bans logs
  routes/security.js               Events, hosts, ingest, SSE stream endpoints
  status/js/security-center.js     Dashboard modal with Overview/Events/Hosts tabs
  SECURITY-FEATURE.md              Full feature documentation
  DEAD-CODE.md, DUP-CODE.md, HARDENING.md   Prior audits

Modified:
  src/app.js                       Mount /api/v1/security/*
  src/utilities/middleware.js      Add ingest endpoints to PUBLIC_ROUTES
  src/security/audit-logger.js     Mirror audit events into security store
  server.js                        Start security workers on boot
  status/build.js                  Bundle security-center.js
  status/index.html                Add Security button to nav

dashcaddy-api/src/app.js

@@ -82,6 +82,7 @@ const dockerResourcesRoutes = require('../routes/docker-resources');
 const eventsRoutes = require('../routes/events');
 const workflowsRoutes = require('../routes/workflows');
 const dependenciesRoutes = require('../routes/dependencies');
+const securityRoutes = require('../routes/security');
 const DependencyManager = require('./managers/dependency-manager');
 const autoRestartRoutes = require('../routes/auto-restart');
 const configDriftRoutes = require('../routes/config-drift');
@@ -638,6 +639,9 @@ async function createApp() {
     asyncHandler: ctx.asyncHandler,
     ok: ctx.ok
   }));
+  apiRouter.use('/security', securityRoutes({
+    log: ctx.log,
+  }));
   apiRouter.use('/dependencies', dependenciesRoutes({
     dependencyManager: ctx.dependencyManager,
     servicesStateManager: ctx.servicesStateManager,