docs: add AI wizard page for wizard feature-flags

[fristovic]

Executive summary

The Feature Flags installation page ran the default wizard (npx @posthog/wizard). That command installs product analytics. It does not add the cheap flags path.

This PR adds /docs/feature-flags/installation/ai-wizard for npx @posthog/wizard feature-flags. The URL slot matches Product Analytics and Web Analytics (/docs/<product>/installation/ai-wizard). The page is not their thin default-wizard wrapper. It documents the specialist command the way MCP Analytics documents command="mcp-analytics".

Paired with wizard #1192 and context-mill #378. The command is not on npm @latest until those merge. The page says that.

cc @team-wizard-and-docs

What changed

• New page: contents/docs/feature-flags/installation/ai-wizard.mdx
• Nav: Feature Flags → Installation → AI wizard (after Overview, same slot as Product Analytics)
• Installation index: <WizardCommand command="feature-flags" /> plus a pointer at the new page
• Start here: first QuestLog item for Next.js App Router
• AI wizard commands table: wizard feature-flags row

Do not add this URL to mill shared_docs until https://posthog.com/docs/feature-flags/installation/ai-wizard.md returns 200. A 404 fails mill CI.

No tour: content PR (contents/ plus nav).

Checklist

• Docs / content style guides
• American English
• Relative URLs for internal links
• Vercel / Cloudflare preview — fork PRs skip deploy-preview.yml. Review http://localhost:8001 or the screenshots below
• No page move, no vercel.json redirect

Reviewer's guide

Testing done

Check	Command / method	Result
Format	lint-staged on commit (prettier, eslint, markdownlint-cli2 --fix); scripts/fix-mdx.js on the new MDX	Commit succeeded
Dev server	pnpm start (Node 22.12.0, GATSBY_MINIMAL=true) at http://localhost:8001	/docs/feature-flags/installation/ai-wizard, /docs/feature-flags/installation, /docs/feature-flags/start-here return 200 and render
Console	Puppeteer pageerror / console.error on live posthog.com (before) vs localhost (after)	One new warning: validateDOMNesting: <ul> cannot appear as a descendant of <p> (MDX list wrapping). SVG width="auto" and WizardCommand-in-<p> were already on the live installation page
Window resize	Viewport 640 (narrow) and 1440 (wide)	Layout reflows. Docs window still usable

Not tested: production build (pnpm build) — memory. Cloudflare preview — fork skip. gh pr-assets upload to PostHog/pr-assets — this fork has no CreateCommitOnBranch there. Screenshots are on fristovic/pr-assets at SHA e07ed7bcfaca3ba15e55df82612834ccec5069b1.

Screenshots

Before = live posthog.com. After = localhost:8001 on this branch.

Installation (wrong-command fix + nav child in the platform grid)

State	Before	After
Light, narrow window
Light, wide window
Dark, narrow window
Dark, wide window

Start here (new first QuestLog item)

State	Before	After
Light, narrow window
Light, wide window
Dark, narrow window
Dark, wide window

New page /docs/feature-flags/installation/ai-wizard

Live URL is 404 today. After only:

State	After
Light, narrow window
Light, wide window
Dark, narrow window
Dark, wide window

What to look at

1. Installation WizardCommand now uses command="feature-flags". Same pattern as AI Observability. Other stacks still have the platform grid.
2. The new page is a real walkthrough, not import WizardInstall. Product Analytics ai-wizard.mdx only wraps the default wizard. Flags needs the specialist command and a pasteable URL.
3. "Not on npm @latest yet" callout names wizard Add anchors to MDX docs #1192 and mill Improve Segment Docs #378. Delete that box after those merge.