docs: add monitoring alerting updates

docs/decisions.md

@@ -459,6 +459,7 @@ Deploy a dedicated monitoring Docker stack using:
 * Grafana for visualization
 * Node Exporter for host metrics
 * cAdvisor for Docker metrics
+* Alertmanager for alert routing and incident notifications
 
 Reason:
 
@@ -466,6 +467,7 @@ Reason:
 * Grafana provides flexible dashboards and datasource integration.
 * Node Exporter provides host CPU, memory and disk visibility.
 * cAdvisor provides Docker container visibility.
+* Alertmanager provides grouping, deduplication and multi-recipient email routing.
 
 Status:
 
@@ -479,6 +481,7 @@ Validation:
 * Prometheus targets validated
 * Grafana datasource connected to Prometheus
 * Initial monitoring dashboards created and validated
+* Alertmanager email routing validated
 
 ---
 
@@ -490,9 +493,10 @@ Export SilverLinux backup metrics through the Node Exporter Textfile Collector.
 
 Metrics:
 
-* Backup success
-* Backup duration
-* Backup size
+* `silverlinux_backup_success`
+* `silverlinux_backup_duration_seconds`
+* `silverlinux_backup_size_bytes`
+* `silverlinux_backup_timestamp_seconds`
 
 Reason:
 
@@ -508,11 +512,11 @@ Implemented
 
 ---
 
-## 2026-06-25 - Validate Backup v2 And Restore Workflow
+## 2026-06-25 - Validate Backup v5.3 And Restore Workflow
 
 Decision:
 
-Treat Backup v2 as the operational SilverLinux backup system.
+Treat Backup v5.3 as the operational SilverLinux backup system.
 
 Implemented:
 
@@ -525,6 +529,10 @@ Implemented:
 * Backup metrics
 * Automatic low disk space cleanup
 * Daily cron execution
+* Lock file protection
+* Disk space validation
+* Central logging
+* Structured failure handling
 
 Validation:
 
@@ -545,6 +553,36 @@ Implemented
 
 ---
 
+## 2026-06-25 - Implement Incident Intelligence Alerting
+
+Decision:
+
+Use Alertmanager with incident grouping, severity-based routing and alert deduplication for SilverLinux monitoring.
+
+Incident groups:
+
+* `backup_failure`
+* `system_pressure`
+* `storage_pressure`
+* `database_outage`
+* `monitoring_failure`
+* `container_health`
+
+Reason:
+
+* Merge related alerts into single incidents.
+* Reduce notification noise.
+* Route alerts by severity.
+* Make alerts root-cause oriented.
+
+Status:
+
+```text
+Implemented
+```
+
+---
+
 ## Future Decisions
 
 Document future decisions using the following template: