fix(web): render full document content, keep graph connected under categories

Two fixes to the new category taxonomy:

- Knowledge Base couldn't show a document/investigation/runbook's own
  markdown body — knowledge_entities.content was never exposed by any
  endpoint (GetEntityKnowledge answers "what knowledge references this
  entity", not "what is this entity's content"). Add GET
  /api/v1/knowledge/content/{id} and render it with the existing
  marked+DOMPurify pipeline in a new Content section.

- The graph hid any edge whose other endpoint wasn't in the active
  category, so nodes with only cross-category neighbors rendered as
  disconnected dots. Queried the real relationship table: ~70% of infra
  edges cross Fleet/Network/Services/Storage lines (compute+network+
  software+storage+physical used to be one "infrastructure" layer).
  EntityGraph now keeps 1-hop neighbors visible but dimmed instead of
  hiding them, so the edges — and what they connect to — stay visible.

- categories.ts: `cognition` domain conflated true knowledge (document/
  investigation/runbook, 58 entities) with operational telemetry
  (execution/check/task/signal/approval/pattern/skill/classification/
  feedback, 300+ entities with their own Operations/Signals/Learning
  pages). Mapping the whole domain to Knowledge pulled in 245 execution
  entities fanning out from ~17 compute nodes via `targets` edges — the
  single biggest source of graph clutter. Knowledge now maps by type
  (document/investigation/runbook only); the rest of cognition is
  excluded from Knowledge Base browsing entirely.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/lib/components/EntityDetailContent.svelte

@@ -2,6 +2,8 @@
   import { onMount, tick } from 'svelte'
   import uPlot from 'uplot'
   import 'uplot/dist/uPlot.min.css'
+  import { marked } from 'marked'
+  import DOMPurify from 'dompurify'
   import {
     fetchEntity,
     fetchGraph,
@@ -10,6 +12,7 @@
     fetchEntitySignals,
     fetchEntityTasks,
     fetchEntityKnowledge,
+    fetchKnowledgeContent,
     fetchChecksForTarget,
     fetchAgentActivity,
     fetchAudit,
@@ -23,6 +26,7 @@
     type Signal,
     type EntityTask,
     type KnowledgeHit,
+    type KnowledgeContent,
     type Check,
     type AgentActivity,
     type AuditEntry
@@ -35,6 +39,8 @@
   import { Skeleton } from '$lib/components/ui/skeleton'
   import { toast } from 'svelte-sonner'
 
+  const KNOWLEDGE_TYPES = new Set(['document', 'investigation', 'runbook'])
+
   let { slug, onSelectEntity }: { slug: string; onSelectEntity?: (slug: string) => void } = $props()
 
   let entity = $state<Entity | null>(null)
@@ -44,6 +50,7 @@
   let signals = $state<Signal[]>([])
   let tasks = $state<EntityTask[]>([])
   let knowledge = $state<KnowledgeHit[]>([])
+  let ownContent = $state<KnowledgeContent | null>(null)
   let checks = $state<Check[]>([])
   let agentActivity = $state<AgentActivity[]>([])
   let auditEntries = $state<AuditEntry[]>([])
@@ -58,13 +65,14 @@
       loading = false
       return
     }
-    const [graphView, m, ev, sig, tk, kh, ch, aa, au] = await Promise.all([
+    const [graphView, m, ev, sig, tk, kh, oc, ch, aa, au] = await Promise.all([
       fetchGraph({ root: entity.id, depth: 1 }),
       fetchMetrics(entity.id),
       fetchEntityEvents(entity.id),
       fetchEntitySignals(entity.id),
       fetchEntityTasks(entity),
       fetchEntityKnowledge(entity.id),
+      KNOWLEDGE_TYPES.has(entity.type) ? fetchKnowledgeContent(entity.id) : Promise.resolve(null),
       fetchChecksForTarget(entity.slug),
       fetchAgentActivity({ entity_id: entity.id, limit: 50 }),
       fetchAudit({ entity_id: entity.id, limit: 50 })
@@ -75,6 +83,7 @@
     signals = sig
     tasks = tk
     knowledge = kh
+    ownContent = oc
     checks = ch
     agentActivity = aa
     auditEntries = au
@@ -210,6 +219,10 @@
     | { key: string; kind: 'flat-object'; value: Record<string, unknown> }
     | { key: string; kind: 'simple'; value: unknown }
 
+  function renderMarkdown(text: string): string {
+    return DOMPurify.sanitize(marked.parse(text, { async: false }) as string)
+  }
+
   function classifyAttributes(attrs: Record<string, unknown>): AttributeRow[] {
     return Object.entries(attrs).map(([key, value]): AttributeRow => {
       if (typeof value === 'string' && (LONG_TEXT_KEYS.has(key) || value.length > 120)) {
@@ -300,6 +313,15 @@
       </div>
     {/snippet}
 
+    {#snippet contentContent()}
+      {#if ownContent}
+        <!-- eslint-disable-next-line svelte/no-at-html-tags — sanitized via DOMPurify -->
+        <div class="prose-chat max-w-none text-xs">{@html renderMarkdown(ownContent.content)}</div>
+      {:else}
+        <p class="text-xs text-muted-foreground">No content.</p>
+      {/if}
+    {/snippet}
+
     {#snippet attributesContent()}
       {#if entity.attributes && Object.keys(entity.attributes).length}
         {@const rows = classifyAttributes(entity.attributes)}
@@ -521,6 +543,7 @@
     {/snippet}
 
     {@const sections = [
+      ...(ownContent ? [{ key: 'content', title: 'Content', count: 1, content: contentContent }] : []),
       { key: 'details', title: 'Details', count: 1, content: detailsContent },
       { key: 'monitoring', title: 'Monitoring', count: checks.length, content: monitoringContent },
       { key: 'attributes', title: 'Attributes', count: Object.keys(entity.attributes ?? {}).length, content: attributesContent },
@@ -541,3 +564,67 @@
     {/each}
   {/if}
 </div>
+
+<style>
+  /* Minimal markdown styling for document/investigation/runbook content —
+     mirrors Chat.svelte's .prose-chat (Svelte scopes styles per-component,
+     so it can't be shared directly). */
+  .prose-chat :global(p) {
+    margin: 0 0 0.5rem;
+  }
+  .prose-chat :global(p:last-child) {
+    margin-bottom: 0;
+  }
+  .prose-chat :global(ul),
+  .prose-chat :global(ol) {
+    margin: 0 0 0.5rem;
+    padding-left: 1.25rem;
+  }
+  .prose-chat :global(li) {
+    margin-bottom: 0.125rem;
+  }
+  .prose-chat :global(code) {
+    background: var(--muted);
+    border-radius: 4px;
+    padding: 0.1em 0.35em;
+    font-family: var(--font-mono);
+    font-size: 0.85em;
+  }
+  .prose-chat :global(pre) {
+    background: var(--muted);
+    border: 1px solid var(--border);
+    border-radius: 8px;
+    padding: 0.625rem 0.75rem;
+    overflow-x: auto;
+    margin: 0 0 0.5rem;
+  }
+  .prose-chat :global(pre code) {
+    background: none;
+    padding: 0;
+    font-size: 0.8125rem;
+  }
+  .prose-chat :global(h1),
+  .prose-chat :global(h2),
+  .prose-chat :global(h3) {
+    font-weight: 600;
+    margin: 0.75rem 0 0.375rem;
+    font-size: 1em;
+  }
+  .prose-chat :global(table) {
+    border-collapse: collapse;
+    margin: 0 0 0.5rem;
+    font-size: 0.8125rem;
+  }
+  .prose-chat :global(th),
+  .prose-chat :global(td) {
+    border: 1px solid var(--border);
+    padding: 0.25rem 0.5rem;
+    text-align: left;
+  }
+  .prose-chat :global(blockquote) {
+    border-left: 3px solid var(--border);
+    padding-left: 0.75rem;
+    color: var(--muted-foreground);
+    margin: 0 0 0.5rem;
+  }
+</style>