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/pages/Knowledge.svelte

@@ -0,0 +1,91 @@
+<script lang="ts">
+  import { searchKnowledge, type KnowledgeHit } from '$lib/api'
+  import * as Card from '$lib/components/ui/card'
+  import { Badge } from '$lib/components/ui/badge'
+  import { Input } from '$lib/components/ui/input'
+  import { Button } from '$lib/components/ui/button'
+  import { ScrollArea } from '$lib/components/ui/scroll-area'
+  import SearchIcon from '@lucide/svelte/icons/search'
+
+  let query = $state('')
+  let results = $state<KnowledgeHit[]>([])
+  let loading = $state(false)
+  let searched = $state(false)
+
+  async function search() {
+    if (!query.trim()) return
+    loading = true
+    results = await searchKnowledge(query)
+    loading = false
+    searched = true
+  }
+
+  function typeVariant(type: string): 'default' | 'secondary' | 'outline' {
+    if (type === 'runbook') return 'secondary'
+    if (type === 'investigation') return 'default'
+    return 'outline'
+  }
+</script>
+
+<div class="flex h-full flex-col gap-4 p-6">
+  <h1 class="text-lg font-semibold">Knowledge search</h1>
+
+  <form
+    onsubmit={(e) => {
+      e.preventDefault()
+      search()
+    }}
+    class="flex gap-2"
+  >
+    <div class="relative flex-1 max-w-lg">
+      <SearchIcon class="absolute left-2.5 top-1/2 size-4 -translate-y-1/2 text-muted-foreground" />
+      <Input
+        placeholder="Search documents, runbooks, investigations…"
+        bind:value={query}
+        class="pl-8"
+      />
+    </div>
+    <Button type="submit" disabled={loading || !query.trim()}>
+      {loading ? 'Searching…' : 'Search'}
+    </Button>
+  </form>
+
+  {#if searched}
+    <p class="text-sm text-muted-foreground">{results.length} result{results.length === 1 ? '' : 's'}{query ? ` for "${query}"` : ''}</p>
+  {/if}
+
+  <ScrollArea class="flex-1">
+    <div class="flex flex-col gap-3 pr-4">
+      {#each results as hit (hit.id)}
+        <Card.Root class="cursor-pointer transition-colors hover:bg-muted/50">
+          <Card.Header>
+            <div class="flex items-center gap-2">
+              <Card.Title class="text-sm">{hit.title}</Card.Title>
+              <Badge variant={typeVariant(hit.type)}>{hit.type}</Badge>
+            </div>
+            {#if hit.snippet}
+              <Card.Description class="text-xs">{@html hit.snippet}</Card.Description>
+            {/if}
+            {#if hit.linked_entities?.length}
+              <div class="mt-1 flex flex-wrap gap-1">
+                {#each hit.linked_entities as slug}
+                  <button
+                    type="button"
+                    class="font-mono text-xs text-muted-foreground underline"
+                    onclick={() => (location.hash = '#/entity/' + encodeURIComponent(slug))}
+                  >
+                    {slug}
+                  </button>
+                {/each}
+              </div>
+            {/if}
+          </Card.Header>
+        </Card.Root>
+      {:else}
+        {#if searched && !loading}
+          <p class="py-12 text-center text-muted-foreground">No results found.</p>
+        {/if}
+      {/each}
+    </div>
+  </ScrollArea>
+</div>