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/EmptyState.svelte

@@ -0,0 +1,17 @@
+<script lang="ts">
+  let {
+    message = 'No items.',
+    colspan = 999,
+    class: className
+  }: {
+    message?: string
+    colspan?: number
+    class?: string
+  } = $props()
+</script>
+
+<tr>
+  <td {colspan} class={['py-8 text-center text-muted-foreground', className].filter(Boolean).join(' ')}>
+    {message}
+  </td>
+</tr>