docs: add hidden page on operating self-hosted SDK generation

[devin-ai-integration]

Summary

Adds an SDKs page, Operations and maintenance, for running self-hosted SDK generation day-to-day, and makes the existing Self-hosted SDKs page the single home for all setup.

Setup consolidation (fern/products/sdks/deep-dives/self-hosted.mdx)

• Adds a ## Infrastructure requirements section (Docker runtime, FERN_TOKEN, the two outbound endpoints, output write access).
• Promotes the private-registry content out of the "custom container registry" accordion into a proper ## Private registry setup section: mirror the generator image (docker pull/tag/push), reference it via the image object in generators.yml, authenticate. The Run generation locally step now links to that section.
• Intro cross-links "infrastructure management, SDK distribution" to the operations page.

New page (fern/products/sdks/deep-dives/self-hosted-operations.mdx) — listed under Self-hosting, focused on maintenance + distribution:

• Ongoing maintenance: keeping generator/CLI versions current, computing versions per release, distributing the SDK, rotating credentials. Links back to setup for infrastructure requirements and re-mirroring.
• Distributing to your clients securely (npm-centered): restricted scoped package, OIDC/trusted publishing + provenance, registry-hosting options (private npm scope vs. Verdaccio/GitHub Packages/Artifactory/CodeArtifact), per-client scoped read tokens + client .npmrc, dist-tags/npm deprecate to steer versions, client-side pinning + npm audit signatures, and npm pack tarball delivery for air-gapped clients.

Registered in fern/products/sdks/sdks.yml under the existing Self-hosting section (not hidden). Also fixed a stray http://localhost:3000 link in the setup page.

fern check --warnings passes (0 errors); Vale passes on the edited pages.

Link to Devin session: https://app.devin.ai/sessions/3e0bbfb5d5944f37a17cfa3dadfc2745

[devin-ai-integration]

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[github-actions]

🌿 Preview your docs: https://fern-preview-devin-1784566169-selfhosted-sdk-ops.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/sdks/deep-dives/self-hosted-operations
• learn/sdks/deep-dives/self-hosted