feat(multiplayer): expose allocator quota metrics

deploy/observability/prometheus-rules.yaml

@@ -52,3 +52,21 @@ spec:
               The 5-minute 5xx ratio for operation {{ $labels.operation }}
               has exceeded 1 percent for 5 minutes.
             runbook_url: https://example.invalid/cosmic-clash/runbooks/control-plane-api
+    - name: cosmic-clash.allocator
+      rules:
+        - alert: CosmicClashAllocatorQuotaDenials
+          expr: |
+            sum by (region) (
+              increase(cosmic_clash_allocator_quota_denials_total[15m])
+            ) > 0
+          for: 5m
+          labels:
+            severity: warning
+            owner: allocator
+          annotations:
+            summary: Cosmic Clash allocator quota is denying allocation attempts
+            description: >-
+              The {{ $labels.region }} allocator has denied at least one
+              allocation attempt in the last 15 minutes; verify quota capacity,
+              provider health, and denial-of-wallet activity.
+            runbook_url: https://example.invalid/cosmic-clash/runbooks/allocator-quota