Add a "Disabling features" reference page

[ctondreau]

Why

Pulling Ask AI analytics for the last 30 days (1,115 conversations, 74.5% resolved), "how do I turn off X" is one of the most consistent question clusters on the site. A sample of ~150 queries turned up readers trying to disable the Ask AI button, the MCP server, the API Explorer, Wiremock test generation, the Fern badge, and CSP.

The notable part: several had nearly the right YAML and still couldn't get there. One reader wrote:

Why isn't this disabling the MCP servers and Ask AI search in the docs.yaml file?

page-actions:
  options:
    ask-ai: false
    mcp: false
ai-search: {}

Every setting they used is real and documented. The gap is that they're scattered across Site settings, the API Reference layout page, and the Dashboard, and that ask-ai: false doesn't do what the name suggests.

What

Adds /learn/docs/configuration/disabling-features under Configuration, next to Site settings and Page settings. It's a router page: each entry says what to set and links to the canonical page rather than restating it.

It leads with the confusion the analytics surfaced most:

• Ask Fern is a Dashboard toggle. No docs.yml key disables it.
• page-actions.options.ask-ai: false hides the page action button only. It does not disable Ask Fern.
• ai-search configures Ask Fern; it has no enable/disable property. ai-search: {} leaves it running with defaults.

Two other traps worth naming:

• The MCP server toggle lives under page-actions.options despite controlling an endpoint rather than a button.
• settings.disable-explorer-proxy is not an off switch for the API Explorer — it keeps the Explorer running and bypasses Fern's proxy. Turning the Explorer off is an empty playground.environments list.

Cross-links added from Configuration overview (new card), Site settings (Ask Fern configuration), Ask Fern overview (enable step), and Hiding content (features vs. content).

Scope notes

• Everything on the page is verified against this repo. I dropped one claim I couldn't substantiate: a reader reported playground.environments: [] failing when set on an - api entry inside a tab in a product YAML. That may be a real bug, but I couldn't confirm the mechanism from the docs, so the page doesn't speculate. Worth a separate look.
• Not covered, and not documented anywhere I could find: disabling CSP / setting a custom permissions-policy on the docs site, and disabling Wiremock test generation for the TypeScript SDK generator. Both came up in Ask AI. Removing the Fern badge from generated SDKs is whitelabel in generators.yml, which is SDK product territory rather than this page.
• No zh translation — the zh overlay doesn't mirror every English page, so this follows existing practice.
• fern check not run — the CLI isn't installed in this environment. Links were verified by hand against the YAML config per AGENTS.md, and every anchor target was confirmed to be a real ##/### heading.

Generated with Claude Code

[github-actions]

⚠️ [vale] _{reported by reviewdog 🐶}
[Microsoft.UIVerbs] Use 'select' instead of the input-specific verb 'click'.

[github-actions]

📝 [vale] _{reported by reviewdog 🐶}
[FernStyles.Acronyms] 'PII' has no definition.

[github-actions]

🚫 [vale] _{reported by reviewdog 🐶}
[Microsoft.Contractions] Use 'isn't' instead of 'is not'.

[github-actions]

🌿 Preview your docs: https://fern-preview-docs-disabling-features-reference.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/docs/ai-features/ask-fern/overview
• learn/docs/customization/hiding-content
• learn/docs/configuration/disabling-features
• learn/docs/configuration/overview
• learn/docs/configuration/site-level-settings