refactor(alerting): rename P95_LATENCY_MS → AVG_DURATION_MS to match what stats_1m_route exposes

The evaluator mapped P95_LATENCY_MS to ExecutionStats.avgDurationMs because
stats_1m_route has no p95 column. Exposing the old name implied p95 semantics
operators did not get. Rename to AVG_DURATION_MS makes the contract honest.
Updated RouteMetric enum (with javadoc), evaluator switch, and admin guide.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cameleer-server-core/src/main/java/com/cameleer/server/core/alerting/RouteMetric.java

@@ -1,3 +1,10 @@
 package com.cameleer.server.core.alerting;
 
-public enum RouteMetric { ERROR_RATE, P95_LATENCY_MS, P99_LATENCY_MS, THROUGHPUT, ERROR_COUNT }
+public enum RouteMetric {
+    ERROR_RATE,
+    /** Average execution duration — maps to stats_1m_route.avgDurationMs. */
+    AVG_DURATION_MS,
+    P99_LATENCY_MS,
+    THROUGHPUT,
+    ERROR_COUNT
+}