fix(docs): correct inaccurate autorelease documentation

[Swimburger]

Summary

Fixes inaccuracies in the autorelease docs page and the generators.yml reference page by removing content that doesn't match the actual schema/implementation.

Verified against the source schema (fern-api/fern): autorelease is optional<boolean> at both the global level (GeneratorsConfigurationSchema) and the per-generator level (GeneratorInvocationSchema). There is no object form.

Changes:

• Removed fabricated cron/pull-based detection config — the autorelease.cron.schedule object doesn't exist in the schema. Removed from both the overview page and the reference page (2 accordions).
• Fixed type from boolean | object → boolean in the generators-yml-reference.mdx ParamFields.
• Replaced non-existent versioning types ("calendar-based, integer, or custom") with "semantic version".
• Removed unverifiable claims about pause/confirmation behavior and credential access model.
• Added "Disable autorelease" section — the CLI changelog (2025-12-11) links to #disable-autorelease which didn't exist. The feature itself is real (autorelease: false per-generator).
• Fixed Vale warning — removed "currently" from early access note.

Review & Testing Checklist for Human

• Verify removed claims are actually wrong: I removed "Autorelease pauses and requests confirmation if it's uncertain about the version bump" and "Publishing uses tokens stored in your GitHub Actions secrets—Fern never has access to these credentials." These couldn't be verified in the CLI code, but they could be accurate server-side behaviors. Someone who knows the autorelease backend should confirm these should stay removed.
• Verify the "Disable autorelease" section is accurate: Confirm that setting autorelease: false on a per-generator basis correctly overrides a global autorelease: true.
• Check the preview deployment to confirm the page renders correctly after removing the AccordionGroup wrapper and promoting sections to h3 headings.

Notes

The link in the CLI changelog entry (2025-12-11) to #disable-autorelease should now resolve correctly with the new section added.

Link to Devin session: https://app.devin.ai/sessions/7fbf767547a6450dbdfe5a695801a97c
Requested by: @Swimburger

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[github-actions]

🌿 Preview your docs: https://fern-preview-devin-1774276308-fix-autorelease-docs.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/sdks/overview/autorelease
• learn/sdks/reference/generators-yml

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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.