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

shared/src/error.rs

@@ -4,10 +4,10 @@ use thiserror::Error;
 pub enum SharedError {
     #[error("Serialization error: {message}")]
     Serialization { message: String },
-    
+
     #[error("Invalid metric value: {message}")]
     InvalidMetric { message: String },
-    
+
     #[error("Protocol error: {message}")]
     Protocol { message: String },
 }
@@ -18,4 +18,4 @@ impl From<serde_json::Error> for SharedError {
             message: err.to_string(),
         }
     }
-}
+}