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/button/button.svelte

@@ -0,0 +1,82 @@
+<script lang="ts" module>
+	import { cn, type WithElementRef } from "$lib/utils.js";
+	import type { HTMLAnchorAttributes, HTMLButtonAttributes } from "svelte/elements";
+	import { type VariantProps, tv } from "tailwind-variants";
+
+	export const buttonVariants = tv({
+		base: "focus-visible:border-ring focus-visible:ring-ring/50 aria-invalid:ring-destructive/20 dark:aria-invalid:ring-destructive/40 aria-invalid:border-destructive dark:aria-invalid:border-destructive/50 rounded-md border border-transparent bg-clip-padding text-sm font-medium focus-visible:ring-3 active:not-aria-[haspopup]:translate-y-px aria-invalid:ring-3 [&_svg:not([class*='size-'])]:size-4 group/button inline-flex shrink-0 items-center justify-center whitespace-nowrap transition-all outline-none select-none disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg]:shrink-0",
+		variants: {
+			variant: {
+				default: "bg-primary text-primary-foreground hover:bg-primary/80",
+				outline: "border-border bg-background hover:bg-muted hover:text-foreground dark:bg-input/30 dark:border-input dark:hover:bg-input/50 aria-expanded:bg-muted aria-expanded:text-foreground shadow-xs",
+				secondary: "bg-secondary text-secondary-foreground hover:bg-secondary/80 aria-expanded:bg-secondary aria-expanded:text-secondary-foreground",
+				ghost: "hover:bg-muted hover:text-foreground dark:hover:bg-muted/50 aria-expanded:bg-muted aria-expanded:text-foreground",
+				destructive: "bg-destructive/10 hover:bg-destructive/20 focus-visible:ring-destructive/20 dark:focus-visible:ring-destructive/40 dark:bg-destructive/20 text-destructive focus-visible:border-destructive/40 dark:hover:bg-destructive/30",
+				link: "text-primary underline-offset-4 hover:underline",
+			},
+			size: {
+				default: "h-9 gap-1.5 px-2.5 in-data-[slot=button-group]:rounded-md has-data-[icon=inline-end]:pr-2 has-data-[icon=inline-start]:pl-2",
+				xs: "h-6 gap-1 rounded-[min(var(--radius-md),8px)] px-2 text-xs in-data-[slot=button-group]:rounded-md has-data-[icon=inline-end]:pr-1.5 has-data-[icon=inline-start]:pl-1.5 [&_svg:not([class*='size-'])]:size-3",
+				sm: "h-8 gap-1 rounded-[min(var(--radius-md),10px)] px-2.5 in-data-[slot=button-group]:rounded-md has-data-[icon=inline-end]:pr-1.5 has-data-[icon=inline-start]:pl-1.5",
+				lg: "h-10 gap-1.5 px-2.5 has-data-[icon=inline-end]:pr-2 has-data-[icon=inline-start]:pl-2",
+				icon: "size-9",
+				"icon-xs": "size-6 rounded-[min(var(--radius-md),8px)] in-data-[slot=button-group]:rounded-md [&_svg:not([class*='size-'])]:size-3",
+				"icon-sm": "size-8 rounded-[min(var(--radius-md),10px)] in-data-[slot=button-group]:rounded-md",
+				"icon-lg": "size-10",
+			},
+		},
+		defaultVariants: {
+			variant: "default",
+			size: "default",
+		},
+	});
+
+	export type ButtonVariant = VariantProps<typeof buttonVariants>["variant"];
+	export type ButtonSize = VariantProps<typeof buttonVariants>["size"];
+
+	export type ButtonProps = WithElementRef<HTMLButtonAttributes> &
+		WithElementRef<HTMLAnchorAttributes> & {
+			variant?: ButtonVariant;
+			size?: ButtonSize;
+		};
+</script>
+
+<script lang="ts">
+	let {
+		class: className,
+		variant = "default",
+		size = "default",
+		ref = $bindable(null),
+		href = undefined,
+		type = "button",
+		disabled,
+		children,
+		...restProps
+	}: ButtonProps = $props();
+</script>
+
+{#if href}
+	<a
+		bind:this={ref}
+		data-slot="button"
+		class={cn(buttonVariants({ variant, size }), className)}
+		href={disabled ? undefined : href}
+		aria-disabled={disabled}
+		role={disabled ? "link" : undefined}
+		tabindex={disabled ? -1 : undefined}
+		{...restProps}
+	>
+		{@render children?.()}
+	</a>
+{:else}
+	<button
+		bind:this={ref}
+		data-slot="button"
+		class={cn(buttonVariants({ variant, size }), className)}
+		{type}
+		{disabled}
+		{...restProps}
+	>
+		{@render children?.()}
+	</button>
+{/if}