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/label/label.svelte

@@ -0,0 +1,20 @@
+<script lang="ts">
+	import { Label as LabelPrimitive } from "bits-ui";
+	import { cn } from "$lib/utils.js";
+
+	let {
+		ref = $bindable(null),
+		class: className,
+		...restProps
+	}: LabelPrimitive.RootProps = $props();
+</script>
+
+<LabelPrimitive.Root
+	bind:ref
+	data-slot="label"
+	class={cn(
+		"gap-2 text-sm leading-none font-medium group-data-[disabled=true]:opacity-50 peer-disabled:opacity-50 flex items-center select-none group-data-[disabled=true]:pointer-events-none peer-disabled:cursor-not-allowed",
+		className
+	)}
+	{...restProps}
+/>