feat(metrics): add model alias resolution metrics

- model_alias_resolution_total: track resolution methods and cache hits
- model_alias_resolution_duration_seconds: measure resolution performance
- model_alias_conflict_total: monitor alias conflicts across GlobalModels

src/core/metrics.py

@@ -44,3 +44,24 @@ health_open_circuits = Gauge(
     "health_open_circuits",
     "Number of provider keys currently in circuit breaker open state",
 )
+
+# 模型别名解析相关
+model_alias_resolution_total = Counter(
+    "model_alias_resolution_total",
+    "Total number of model alias resolutions",
+    ["method", "cache_hit"],
+    # method: direct_match, provider_model_name, alias, not_found
+    # cache_hit: true, false
+)
+
+model_alias_resolution_duration_seconds = Histogram(
+    "model_alias_resolution_duration_seconds",
+    "Duration of model alias resolution in seconds",
+    ["method"],
+    buckets=[0.001, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0],  # 1ms 到 1s
+)
+
+model_alias_conflict_total = Counter(
+    "model_alias_conflict_total",
+    "Total number of alias conflicts detected (same alias maps to multiple GlobalModels)",
+)