feat(web): adopt @vincjo/datatables for all tables, standardize shared components

- Add DataTable.svelte: declarative columns, built-in sorting, sticky headers,
  text truncation, column alignment, configurable widths, optional pagination/search
- 12 built-in renderers: BadgeRenderer, StatusBadgeRenderer (unified risk/severity/
  execution/state/type variant mapping), HealthDotRenderer, RelativeTimeRenderer,
  DateRenderer, DurationRenderer, StatusDotRenderer, SignalActions, ApprovalActions,
  ActivityAction, ActivityCancel
- Migrate Overview (task board), Signals, Ops (3 tables) to DataTable
- Refactor EntityTable treegrid to use shared SortHeader, EmptyState, HealthDotRenderer
- Create shared components: EmptyState, StatusBadge, FilterTabs
- Clean up Knowledge.svelte: replace inline relTime() and typeVariant() with shared utils
- Add width, align, truncate column props; table-fixed layout; rounded-xl borders
- Bump version to 0.11.0

web/src/lib/components/data-table/renderers/ActivityCancel.svelte

@@ -0,0 +1,22 @@
+<script lang="ts">
+  import { Button } from '$lib/components/ui/button'
+  import type { ActivityItem } from '$lib/api'
+
+  let {
+    row,
+    onCancel
+  }: {
+    row: ActivityItem
+    onCancel?: (id: string) => void
+  } = $props()
+
+  function showCancel(status: string): boolean {
+    return ['pending_approval', 'approved', 'running'].includes(status)
+  }
+</script>
+
+<div class="flex justify-end">
+  {#if showCancel(row.status)}
+    <Button size="sm" variant="outline" onclick={() => onCancel?.(row.id)}>Cancel</Button>
+  {/if}
+</div>