feat(observability): ✨ comprehensive platform alert rules

Replace ad-hoc forgejo/disk alerts with structured VMRule covering:
- platform-health: ForgejoDown, IngressHighErrorRate, NodeNotReady, PodCrashLooping
- storage: PVCUsageHigh (>80%), PVCUsageCritical (>90%)
- resources: NodeCPUHigh (>85%), NodeMemoryHigh (>90%)

otc/observability.buildth.ing/stacks/observability/victoria-k8s-stack/manifests/alerts.yaml

@@ -1,40 +1,95 @@
 apiVersion: operator.victoriametrics.com/v1beta1
 kind: VMRule
 metadata:
-  name: forgejo-alerts
+  name: edp-platform-alerts
   namespace: observability
 spec:
   groups:
-    - name: forgejo
+    - name: platform-health
       rules:
-        - alert: forgejo down
-          expr: sum by(cluster_environment) (up{pod=~"forgejo-server-.*"}) < 1
-          for: 30s
+        - alert: ForgejoDown
+          expr: sum by(cluster_environment) (up{job="forgejo-server-http"}) < 1
+          for: 1m
           labels:
             severity: critical
-            job:  "{{ $labels.job }}"
           annotations:
-            value: "{{ $value }}"
-            description: 'forgejo is down in cluster environment {{ $labels.cluster_environment }}'
-    - name: forgejo-backup
-      rules:
-        - alert: forgejo s3 backup job failed
-          expr: max by(cluster_environment) (kube_job_status_failed{job_name=~"forgejo-s3-backup-.*"}) != 0
-          for: 30s
-          labels:
-            severity: critical
-            job:  "{{ $labels.job }}"
-          annotations:
-            value: "{{ $value }}"
-            description: 'forgejo s3 backup job failed in cluster environment {{ $labels.cluster_environment }}'
-    - name: disk-consumption-high
-      rules:
-        - alert: disk consumption high
-          expr: 1-(kubelet_volume_stats_available_bytes / kubelet_volume_stats_capacity_bytes) > 0.6
-          for: 30s
+            summary: "Forgejo is down on {{ $labels.cluster_environment }}"
+            description: "Forgejo server has been unreachable for more than 1 minute in cluster {{ $labels.cluster_environment }}."
+
+        - alert: IngressHighErrorRate
+          expr: |
+            sum by(cluster_environment) (rate(nginx_ingress_controller_requests{status=~"5.."}[5m]))
+            / sum by(cluster_environment) (rate(nginx_ingress_controller_requests[5m])) > 0.05
+          for: 5m
           labels:
             severity: major
-            job:  "{{ $labels.job }}"
           annotations:
-            value: "{{ $value }}"
-            description: 'disk consumption of pvc {{ $labels.namespace }}/{{ $labels.persistentvolumeclaim }} is high in cluster environment {{ $labels.cluster_environment }}'
+            summary: "High ingress 5xx rate on {{ $labels.cluster_environment }}"
+            description: "More than 5% of ingress requests are returning 5xx errors for over 5 minutes."
+            value: "{{ $value | humanizePercentage }}"
+
+        - alert: NodeNotReady
+          expr: kube_node_status_condition{condition="Ready", status="true"} == 0
+          for: 5m
+          labels:
+            severity: critical
+          annotations:
+            summary: "Node {{ $labels.node }} not ready on {{ $labels.cluster_environment }}"
+            description: "Node {{ $labels.node }} has been in NotReady state for more than 5 minutes."
+
+        - alert: PodCrashLooping
+          expr: rate(kube_pod_container_status_restarts_total[15m]) * 60 * 15 > 3
+          for: 5m
+          labels:
+            severity: major
+          annotations:
+            summary: "Pod {{ $labels.namespace }}/{{ $labels.pod }} crash-looping on {{ $labels.cluster_environment }}"
+            description: "Pod has restarted more than 3 times in the last 15 minutes."
+
+    - name: storage
+      rules:
+        - alert: PVCUsageHigh
+          expr: |
+            1 - (kubelet_volume_stats_available_bytes / kubelet_volume_stats_capacity_bytes) > 0.80
+          for: 5m
+          labels:
+            severity: major
+          annotations:
+            summary: "PVC {{ $labels.namespace }}/{{ $labels.persistentvolumeclaim }} usage >80%"
+            description: "PVC usage is at {{ $value | humanizePercentage }} on {{ $labels.cluster_environment }}."
+            value: "{{ $value | humanizePercentage }}"
+
+        - alert: PVCUsageCritical
+          expr: |
+            1 - (kubelet_volume_stats_available_bytes / kubelet_volume_stats_capacity_bytes) > 0.90
+          for: 5m
+          labels:
+            severity: critical
+          annotations:
+            summary: "PVC {{ $labels.namespace }}/{{ $labels.persistentvolumeclaim }} usage >90%"
+            description: "PVC is almost full at {{ $value | humanizePercentage }} on {{ $labels.cluster_environment }}. Immediate action required."
+            value: "{{ $value | humanizePercentage }}"
+
+    - name: resources
+      rules:
+        - alert: NodeCPUHigh
+          expr: |
+            1 - avg by(instance, cluster_environment) (rate(node_cpu_seconds_total{mode="idle"}[5m])) > 0.85
+          for: 15m
+          labels:
+            severity: major
+          annotations:
+            summary: "Node {{ $labels.instance }} CPU >85% on {{ $labels.cluster_environment }}"
+            description: "Node CPU utilization has been above 85% for 15 minutes."
+            value: "{{ $value | humanizePercentage }}"
+
+        - alert: NodeMemoryHigh
+          expr: |
+            1 - (node_memory_MemAvailable_bytes / node_memory_MemTotal_bytes) > 0.90
+          for: 10m
+          labels:
+            severity: major
+          annotations:
+            summary: "Node memory >90% on {{ $labels.cluster_environment }}"
+            description: "Node memory utilization above 90% for 10 minutes."
+            value: "{{ $value | humanizePercentage }}"