fix(alerts): final sweep — drop ACKNOWLEDGED from AlertStateChip + CMD-K; harden V17 IT

UI: AlertStateChip.LABELS and .COLORS no longer include ACKNOWLEDGED
(dropped in V17). AlertStateChip.test.tsx test-cases trimmed to the
three remaining states. LayoutShell CMD-K now searches FIRING alerts
with acked=false (was state=[FIRING,ACKNOWLEDGED]).

Test: V17MigrationIT.open_rule_index_predicate_is_reworked replaced
with a structural-only assertion (index exists, indisunique). The
pg_get_indexdef pretty-printer varies across Postgres versions, so
predicate semantics are verified behaviorally in
PostgresAlertInstanceRepositoryIT (findOpenForRule_* +
save_rejectsSecondOpenInstanceForSameRuleAndExchange).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/components/LayoutShell.tsx

@@ -368,7 +368,7 @@ function LayoutContent() {
   const { data: envRecords = [] } = useEnvironments();
 
   // Open alerts + rules for CMD-K (env-scoped).
-  const { data: cmdkAlerts } = useAlerts({ state: ['FIRING', 'ACKNOWLEDGED'], limit: 100 });
+  const { data: cmdkAlerts } = useAlerts({ state: ['FIRING'], acked: false, limit: 100 });
   const { data: cmdkRules } = useAlertRules();
 
   // Merge environments from both the environments table and agent heartbeats