refactor(search): drop dead SearchIndexer subsystem

After the ExecutionController removal (0f635576), SearchIndexer
subscribed to ExecutionUpdatedEvent but nothing publishes that event.
Every SearchIndexerStats metric returned always-zero, and the admin
/api/v1/admin/clickhouse/pipeline endpoint that surfaced those stats
carried no signal.

Backend removed:
- core: SearchIndexer, SearchIndexerStats, ExecutionUpdatedEvent
- app: IndexerPipelineResponse DTO, /pipeline endpoint on
  ClickHouseAdminController (field + ctor param)
- StorageBeanConfig.searchIndexer bean

UI removed:
- IndexerPipeline type + useIndexerPipeline hook in
  api/queries/admin/clickhouse.ts
- Indexer Pipeline card in ClickHouseAdminPage.tsx (plus ProgressBar
  import and pipeline* CSS classes)

OpenAPI schema.d.ts + openapi.json regenerated (stale /pipeline path
and IndexerPipelineResponse schema removed).

SearchIndex interface + ClickHouseSearchIndex impl kept — those are
live and used by SearchService + ExchangeMatchEvaluator.

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

ui/src/api/queries/admin/clickhouse.ts

@@ -38,16 +38,6 @@ export interface ClickHouseQuery {
   query: string;
 }
 
-export interface IndexerPipeline {
-  queueDepth: number;
-  maxQueueSize: number;
-  failedCount: number;
-  indexedCount: number;
-  debounceMs: number;
-  indexingRate: number;
-  lastIndexedAt: string | null;
-}
-
 // ── Query Hooks ────────────────────────────────────────────────────────
 
 export function useClickHouseStatus() {
@@ -86,11 +76,3 @@ export function useClickHouseQueries() {
   });
 }
 
-export function useIndexerPipeline() {
-  const refetchInterval = useRefreshInterval(10_000);
-  return useQuery({
-    queryKey: ['admin', 'clickhouse', 'pipeline'],
-    queryFn: () => adminFetch<IndexerPipeline>('/clickhouse/pipeline'),
-    refetchInterval,
-  });
-}