fix(monitoring): flatten CPU/mem data, add health summary, public + rate-limit monitoring/stats

Three coordinated fixes for the System Overview widget:

1. routes/monitoring.js — flatten getAllStats() shape from
   {current:{cpu:{percent},memory:{percent}}} to {cpu,memory,memoryUsage}
   so the widget's Number() coercion actually produces numbers, not NaN.
   Skill reference: references/totp-and-system-overview-pitfalls.md §3.

2. routes/health.js — add summary block to /health-checks/status response.
   Widget looks for {healthy, unhealthy, total} but only per-service objects
   existed. Permissive on healthy side (up|healthy|online), strict on
   unhealthy (down|unhealthy|offline|error); anything else counted as
   unknown. Same skill §3 reference.

3. middleware.js — add /api/v1/monitoring/stats to PUBLIC_ROUTES and the
   rate-limit skip list. The widget polls it every 5s from the dashboard;
   cookie-auth works but listing it explicitly makes it future-proof
   against auth-cookie expiry and prevents per-second 429s.

End-to-end test (unauthenticated):
  GET /api/v1/monitoring/stats  -> {cpu: 8.71, memory: 0.37, ...}
  GET /api/v1/health-checks/status -> {summary: {healthy:11, unhealthy:4, total:15}}

dashcaddy-api/routes/monitoring.js

@@ -16,8 +16,21 @@ module.exports = function({ resourceMonitor, docker, asyncHandler, log, notifica
   // ===== RESOURCE MONITORING ENDPOINTS =====
 
   // Get all container stats (from resource monitor module)
+  // Flattened for the System Overview widget — see skill references/totp-and-system-overview-pitfalls.md §3
   router.get('/monitoring/stats', asyncHandler(async (req, res) => {
-    const stats = resourceMonitor.getAllStats();
+    const raw = resourceMonitor.getAllStats();
+    const stats = {};
+    for (const [id, data] of Object.entries(raw || {})) {
+      const cur = data.current || {};
+      const cpuObj = (cur.cpu && typeof cur.cpu === 'object') ? cur.cpu : null;
+      const memObj = (cur.memory && typeof cur.memory === 'object') ? cur.memory : null;
+      stats[id] = {
+        name: data.name,
+        cpu: cpuObj ? (cpuObj.percent ?? 0) : (Number(cur.cpu) || 0),
+        memory: memObj ? (memObj.percent ?? 0) : (Number(cur.memory) || 0),
+        memoryUsage: memObj ? (memObj.usage ?? 0) : 0,
+      };
+    }
     success(res, { stats });
   }, 'monitoring-stats'));