PERF(observability): add HA for Loki and Tempo

- Loki: replicas 1→2 with soft anti-affinity
- Tempo: replicas 1→2 with soft anti-affinity
- Thanos/Prometheus: keep replica 1

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tempo/helm-values.yaml

@@ -10,6 +10,20 @@
 # Medium priority for observability
 priorityClassName: medium-priority
 
+# HA with 2 replicas
+replicas: 2
+
+# Soft anti-affinity for HA
+affinity:
+  podAntiAffinity:
+    preferredDuringSchedulingIgnoredDuringExecution:
+      - weight: 100
+        podAffinityTerm:
+          labelSelector:
+            matchLabels:
+              app.kubernetes.io/name: tempo
+          topologyKey: kubernetes.io/hostname
+
 # =============================================================================
 # Resource Limits (optimized for small cluster)
 # =============================================================================