Add sortable table columns, pre-populate date filter, inline command palette

- Table headers are now clickable to sort by column (client-side)
- From date picker defaults to today 00:00 instead of empty
- Command palette expands inline from search bar instead of modal dialog

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

ui/src/pages/executions/use-execution-search.ts

@@ -1,6 +1,14 @@
 import { create } from 'zustand';
 import type { SearchRequest } from '../../api/schema';
 
+function todayMidnight(): string {
+  const d = new Date();
+  d.setHours(0, 0, 0, 0);
+  // Format as datetime-local value: YYYY-MM-DDTHH:mm
+  const pad = (n: number) => n.toString().padStart(2, '0');
+  return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())}T00:00`;
+}
+
 interface ExecutionSearchState {
   status: string[];
   timeFrom: string;
@@ -31,7 +39,7 @@ interface ExecutionSearchState {
 
 export const useExecutionSearch = create<ExecutionSearchState>((set, get) => ({
   status: ['COMPLETED', 'FAILED'],
-  timeFrom: '',
+  timeFrom: todayMidnight(),
   timeTo: '',
   durationMin: null,
   durationMax: null,
@@ -62,7 +70,7 @@ export const useExecutionSearch = create<ExecutionSearchState>((set, get) => ({
   clearAll: () =>
     set({
       status: ['COMPLETED', 'FAILED', 'RUNNING'],
-      timeFrom: '',
+      timeFrom: todayMidnight(),
       timeTo: '',
       durationMin: null,
       durationMax: null,