feat(alerting): Postgres repository for alert_instances with inbox queries

Implements AlertInstanceRepository: save (upsert), findById, findOpenForRule,
listForInbox (3-way OR: user/group/role via && array-overlap + ANY), countUnreadForUser
(LEFT JOIN alert_reads), ack, resolve, markSilenced, deleteResolvedBefore.
Integration test covers all 9 scenarios including inbox fan-out across all
three target types. Also adds @JsonIgnoreProperties(ignoreUnknown=true) to
SilenceMatcher to suppress Jackson serializing isWildcard() as a round-trip field.

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

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

@@ -1,7 +1,10 @@
 package com.cameleer.server.core.alerting;
 
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+
 import java.util.UUID;
 
+@JsonIgnoreProperties(ignoreUnknown = true)
 public record SilenceMatcher(
         UUID ruleId, String appSlug, String routeId, String agentId, AlertSeverity severity) {