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)

frontend/src/components/dashboard/StackHealthTable.tsx

@@ -78,7 +78,7 @@ export function StackHealthTable({ stackStatuses, metrics, onNavigateToStack }:
 
   if (Object.keys(stackStatuses).length === 0) {
     return (
-      <Card className="bg-card">
+      <Card className="bg-card shadow-card-bevel">
         <CardContent className="py-8">
           <div className="flex flex-col items-center justify-center gap-2 text-stat-subtitle">
             <Layers className="h-8 w-8 text-stat-icon" strokeWidth={1.5} />
@@ -90,7 +90,7 @@ export function StackHealthTable({ stackStatuses, metrics, onNavigateToStack }:
   }
 
   return (
-    <Card className="bg-card">
+    <Card className="bg-card shadow-card-bevel">
       <CardHeader className="pb-2">
         <div className="flex items-center justify-between">
           <CardTitle className="text-sm font-medium text-stat-title">Stack Health</CardTitle>