feat(ui): M4 — agent activity, knowledge search, audit, correlation grouping

Add three new pages completing the control-room web UI:
- Agent activity: polls /agent-activity every 5s, filterable by type/agent
- Knowledge search: FTS over /knowledge/search with snippet + entity links
- Audit trail: browseable audit log with actor/action/entity filters

Enhanced live events page with correlation-id clustering (Groups toggle).
Added fetchAgentActivity/searchKnowledge/fetchAudit to the API client.
11 nav items now cover all planned control-room views.

web/src/lib/components/ui/dropdown-menu/dropdown-menu-sub-trigger.svelte

@@ -0,0 +1,29 @@
+<script lang="ts">
+	import { DropdownMenu as DropdownMenuPrimitive } from "bits-ui";
+	import ChevronRightIcon from '@lucide/svelte/icons/chevron-right';
+	import { cn } from "$lib/utils.js";
+
+	let {
+		ref = $bindable(null),
+		class: className,
+		inset,
+		children,
+		...restProps
+	}: DropdownMenuPrimitive.SubTriggerProps & {
+		inset?: boolean;
+	} = $props();
+</script>
+
+<DropdownMenuPrimitive.SubTrigger
+	bind:ref
+	data-slot="dropdown-menu-sub-trigger"
+	data-inset={inset}
+	class={cn(
+		"focus:bg-accent focus:text-accent-foreground data-open:bg-accent data-open:text-accent-foreground not-data-[variant=destructive]:focus:**:text-accent-foreground gap-2 rounded-sm px-2 py-1.5 text-sm data-inset:pl-8 [&_svg:not([class*='size-'])]:size-4 flex cursor-default items-center outline-hidden select-none data-[inset]:pl-8 [&_svg]:pointer-events-none [&_svg]:shrink-0",
+		className
+	)}
+	{...restProps}
+>
+	{@render children?.()}
+	<ChevronRightIcon class="ml-auto" />
+</DropdownMenuPrimitive.SubTrigger>