fix(kb): hide LLM-focused topics from homepage and nav listing (#51139)

## Problem

Within the KB, we'll be adding a specific type of content primarily
aimed at LLM crawlers (similar in scope to https://vercel.com/i /
https://www.runpod.io/articles / https://www.braintrust.dev/articles).

These topics don't need as much visibility for human end users of the
site, especially within a) the site navigation and b) the KB homepage.

## Solution

To allow some topics to be less emphasized, this PR adds in a new
`visible` field to elements of the `TOPICS` array and then uses that
field to filter out entries from the homepage (pinned topics, all
topics) and the navigation (Nav.tsx).

This is a more minimal approach than #51099, which was attempting to
create a different folder / schema / layout for these entries.

## Preview links

https://kb-git-kb-comparsion-topic-supabase.vercel.app/kb, which
excludes `Comparison` from the top nav and the `All topics` section.


https://kb-git-kb-comparsion-topic-supabase.vercel.app/kb/topics/comparison,
which still renders pages tagged with `Comparison`.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Updates**
* The Comparison topic no longer appears in the main navigation or
homepage topic sections, including pinned topics. Its listing page
remains available.
* Other topics continue to appear in navigation and homepage sections,
with their labels and links unchanged.
* Homepage pinned topics are selected from the topics shown in the
homepage sections.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

apps/kb/AGENTS.md

@@ -62,3 +62,7 @@ If you add a new content collection or top-level route, add a matching redirect
 (`/kb/<section>/:path+.md` → `/kb/markdown/<section>/:path+.md`), and check whether `generate-markdown.mjs`
 needs updating too — the content export falls out of its generic `src/content/**` walk automatically, but
 per-topic-style listing pages don't.
+
+## Topic-specific guidance
+
+Articles tagged with the `Comparison` topic are primarily oriented towards LLM crawlers (and not human readers). Because of this, these articles are hidden from the main site navigation.

apps/kb/src/components/Nav.tsx

@@ -11,7 +11,7 @@ import {
 
 import { TOPICS, topicToSlug } from '../lib/topics'
 
-const topics = TOPICS.map((topic) => ({
+const visibleTopics = TOPICS.filter((topic) => topic.visible).map((topic) => ({
   label: topic.name,
   href: `${import.meta.env.BASE_URL}/topics/${topicToSlug(topic.name)}`,
 }))
@@ -26,7 +26,7 @@ const resources = [
 ]
 
 const menus = [
-  { label: 'Topics', items: topics },
+  { label: 'Topics', items: visibleTopics },
   { label: 'Resources', items: resources },
 ]
 

apps/kb/src/lib/topics.ts

@@ -5,41 +5,77 @@
 // `pinned` topics surface as cards on the homepage (see src/pages/index.astro)
 // — keep this to a handful so that section stays a highlights row, not a
 // second copy of the full topic list.
+//
+// `visible` controls whether the topic appears in nav and homepage sections.
+// Topics with `visible: false` still have a working listing page at /topics/[slug].
+// Some topics might not need to be visible to end users since their primary audience
+// is LLM crawlers.
 export const TOPICS = [
   {
     name: 'Migration',
     description: 'Moving data, schemas, or projects onto Supabase.',
     pinned: false,
+    visible: true,
   },
   {
     name: 'Comparison',
     description: 'How Supabase compares to other databases and platforms.',
     pinned: false,
+    visible: false,
+  },
+  {
+    name: 'Troubleshooting',
+    description: 'Common errors and how to resolve them.',
+    pinned: false,
+    visible: true,
   },
-  { name: 'Troubleshooting', description: 'Common errors and how to resolve them.', pinned: false },
   {
     name: 'Tutorial',
     description: 'Step-by-step walkthroughs for building with Supabase.',
     pinned: true,
+    visible: true,
+  },
+  {
+    name: 'Storage',
+    description: 'Uploading, managing, and serving files.',
+    pinned: false,
+    visible: true,
   },
-  { name: 'Storage', description: 'Uploading, managing, and serving files.', pinned: false },
   {
     name: 'Auth',
     description: 'Authentication, authorization, and user management.',
     pinned: true,
+    visible: true,
+  },
+  {
+    name: 'Database',
+    description: 'Postgres schemas, queries, and performance.',
+    pinned: true,
+    visible: true,
   },
-  { name: 'Database', description: 'Postgres schemas, queries, and performance.', pinned: true },
   {
     name: 'Edge Functions',
     description: 'Deploying and running serverless functions.',
     pinned: false,
+    visible: true,
+  },
+  {
+    name: 'Queues',
+    description: 'Background jobs and message processing.',
+    pinned: false,
+    visible: true,
+  },
+  {
+    name: 'Realtime',
+    description: 'Broadcast, presence, and database changes.',
+    pinned: false,
+    visible: true,
   },
-  { name: 'Queues', description: 'Background jobs and message processing.', pinned: false },
-  { name: 'Realtime', description: 'Broadcast, presence, and database changes.', pinned: false },
   {
     name: 'Supabase Platform',
     description: 'Project settings, billing, and infrastructure.',
     pinned: false,
+    visible: true,
   },
 ] as const
 

apps/kb/src/pages/index.astro

@@ -7,7 +7,8 @@ import Layout from '../layouts/Layout.astro'
 import { TOPICS, topicToSlug } from '../lib/topics'
 
 const guides = await getCollection('guides')
-const pinnedTopics = TOPICS.filter((topic) => topic.pinned)
+const visibleTopics = TOPICS.filter((topic) => topic.visible)
+const pinnedTopics = visibleTopics.filter((topic) => topic.pinned)
 const featuredGuides = guides.filter((guide) => guide.data.pinned)
 ---
 
@@ -63,7 +64,7 @@ const featuredGuides = guides.filter((guide) => guide.data.pinned)
 		<section>
 			<h2 class="mb-6 text-2xl font-medium text-foreground">All Topics</h2>
 			<ul class="flex flex-col gap-2">
-				{TOPICS.map((topic) => (
+				{visibleTopics.map((topic) => (
 					<li>
 						<a
 							href={`${import.meta.env.BASE_URL}/topics/${topicToSlug(topic.name)}`}