Server-side sorting for execution search results

Sorting now applies to the entire result set via ClickHouse ORDER BY
instead of only sorting the current page client-side. Default sort
order is timestamp descending. Supported sort columns: startTime,
status, agentId, routeId, correlationId, durationMs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/api/schema.d.ts

@@ -562,6 +562,8 @@ export interface components {
             offset?: number;
             /** Format: int32 */
             limit?: number;
+            sortField?: string;
+            sortDir?: string;
         };
         ExecutionSummary: {
             executionId: string;
@@ -915,6 +917,8 @@ export interface operations {
                 processorType?: string;
                 offset?: number;
                 limit?: number;
+                sortField?: string;
+                sortDir?: string;
             };
             header?: never;
             path?: never;