fix(dashboard): harden real-time dashboard with bug fixes and design compliance (#517)

* fix(dashboard): harden real-time dashboard with bug fixes and design compliance

- Fix host alert spam: add 5-minute cooldown for CPU/RAM/disk threshold
  alerts, preventing duplicate notifications every 30s during sustained
  breaches. Extract shared dispatchWithCooldown helper (also used by
  Docker janitor alerts).
- Fix memory metric inflation: subtract filesystem cache from stored
  memory_mb values, matching the existing calculateMemoryPercent logic.
- Fix crash detection reliability: replace fragile 'seconds ago' string
  matching with a tracked Set of alerted container IDs. Containers are
  only alerted once per crash event, with automatic cleanup when they
  start running again or after a 1-hour TTL.
- Fix health status bar: exited containers now trigger 'degraded' state
  independently of unread error notifications.
- Fix CPU chart Y-axis: auto-scale when aggregate container CPU exceeds
  100% instead of silently clipping at the hardcoded domain ceiling.
- Fix grammar: 'actives' to 'active' in container count label.
- Add shadow-card-bevel to all dashboard cards per design system.
- Update dashboard docs to reflect revised health status thresholds.

* test(dashboard): update monitor service tests for new alert signatures

- Add container Id fields to crash detection test fixtures
- Update host alert assertions to match dispatchWithCooldown 3-arg call
- Fix unhealthy container test to use State: 'unhealthy' instead of
  State: 'running' (running containers are now skipped in crash detect)

docs/features/dashboard.mdx

@@ -16,8 +16,8 @@ The top bar provides an at-a-glance health assessment for the active node. Sench
 | Status | Meaning |
 |--------|---------|
 | **Healthy** | All systems nominal. No resources above warning thresholds, no unread errors. |
-| **Degraded** | At least one resource is above 80%, or there are unread error alerts. |
-| **Critical** | At least one resource is above 90%, or there are exited containers with unread errors. |
+| **Degraded** | At least one resource is above 80%, there are exited containers, or there are unread error alerts. |
+| **Critical** | At least one resource is above 90%, or there are exited containers combined with unread errors. |
 
 The bar also shows the active node name, the number of running containers, and the current alert count.