Implement hysteresis for metric status changes to prevent flapping

Add comprehensive hysteresis support to prevent status oscillation near
threshold boundaries while maintaining responsive alerting.

Key Features:
- HysteresisThresholds with configurable upper/lower limits
- StatusTracker for per-metric status history
- Default gaps: CPU load 10%, memory 5%, disk temp 5°C

Updated Components:
- CPU load collector (5-minute average with hysteresis)
- Memory usage collector (percentage-based thresholds)
- Disk temperature collector (SMART data monitoring)
- All collectors updated to support StatusTracker interface

Cache Interval Adjustments:
- Service status: 60s → 10s (faster response)
- Disk usage: 300s → 60s (more frequent checks)
- Backup status: 900s → 60s (quicker updates)
- SMART data: moved to 600s tier (10 minutes)

Architecture:
- Individual metric status calculation in collectors
- Centralized StatusTracker in MetricCollectionManager
- Status aggregation preserved in dashboard widgets

agent/src/metrics/mod.rs

@@ -1,5 +1,5 @@
 use anyhow::Result;
-use cm_dashboard_shared::Metric;
+use cm_dashboard_shared::{Metric, StatusTracker};
 use std::collections::HashMap;
 use std::time::Instant;
 use tracing::{debug, error, info};
@@ -16,6 +16,7 @@ pub struct MetricCollectionManager {
     collectors: Vec<Box<dyn Collector>>,
     cache_manager: MetricCacheManager,
     last_collection_times: HashMap<String, Instant>,
+    status_tracker: StatusTracker,
 }
 
 impl MetricCollectionManager {
@@ -117,6 +118,7 @@ impl MetricCollectionManager {
             collectors,
             cache_manager,
             last_collection_times: HashMap::new(),
+            status_tracker: StatusTracker::new(),
         })
     }
 
@@ -134,7 +136,7 @@ impl MetricCollectionManager {
         for collector in &self.collectors {
             let collector_name = collector.name();
 
-            match collector.collect().await {
+            match collector.collect(&mut self.status_tracker).await {
                 Ok(metrics) => {
                     info!(
                         "Force collected {} metrics from {} collector",
@@ -200,7 +202,7 @@ impl MetricCollectionManager {
 
             if should_collect {
                 collecting_fresh.insert(collector_name.to_string());
-                match collector.collect().await {
+                match collector.collect(&mut self.status_tracker).await {
                     Ok(metrics) => {
                         // Collector returned fresh metrics (debug logging disabled for performance)