feat(alerting): server-side state+severity filters, ButtonGroup filter UI

Backend: `GET /environments/{envSlug}/alerts` now accepts optional multi-value
`state=…` and `severity=…` query params. Filters are pushed down to
PostgresAlertInstanceRepository, which appends `AND state::text = ANY(?)` /
`AND severity::text = ANY(?)` to the inbox query (null/empty = no filter).

`AlertInstanceRepository.listForInbox` gained a 7-arg overload; the old 5-arg
form is preserved as a default delegate so existing callers (evaluator,
AlertingFullLifecycleIT, PostgresAlertInstanceRepositoryIT) compile unchanged.
`InAppInboxQuery.listInbox` also has a new filtered overload.

UI: InboxPage severity filter migrated from `SegmentedTabs` (single-select,
no color cues) to `ButtonGroup` (multi-select with severity-coloured dots),
matching the topnavbar status-filter pattern. `useAlerts` forwards the
filters as query params and cache-keys on the filter tuple so each combo
is independently cached.

Unit + hook tests updated to the new contract (5 UI tests + 8 Java unit
tests passing). OpenAPI types regenerated from the fresh local backend.

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

@@ -10,10 +10,30 @@ public interface AlertInstanceRepository {
     AlertInstance save(AlertInstance instance);   // upsert by id
     Optional<AlertInstance> findById(UUID id);
     Optional<AlertInstance> findOpenForRule(UUID ruleId);  // state IN ('PENDING','FIRING','ACKNOWLEDGED')
+
+    /**
+     * Unfiltered inbox listing. Convenience overload that delegates to the filtered
+     * variant with {@code states}/{@code severities} set to {@code null} (no filter).
+     */
+    default List<AlertInstance> listForInbox(UUID environmentId,
+                                             List<String> userGroupIdFilter,
+                                             String userId,
+                                             List<String> userRoleNames,
+                                             int limit) {
+        return listForInbox(environmentId, userGroupIdFilter, userId, userRoleNames, null, null, limit);
+    }
+
+    /**
+     * Inbox listing with optional state + severity filters. {@code null} or empty lists mean
+     * "no filter on that field". When both lists are non-empty the row must match at least one
+     * value from each list (AND between dimensions, OR within).
+     */
     List<AlertInstance> listForInbox(UUID environmentId,
                                      List<String> userGroupIdFilter,
                                      String userId,
                                      List<String> userRoleNames,
+                                     List<AlertState> states,
+                                     List<AlertSeverity> severities,
                                      int limit);
 
     /**