Convert SDKs section headings to sentence case

Summary

Converted all page titles, card titles, and component headings in the SDKs documentation section from title case to sentence case for consistency with documentation standards. This includes:

• Page titles in frontmatter (23 files)
• Card titles in the capabilities overview page
• Guide page titles (configure auto-pagination, configure global headers, etc.)
• Language-specific quickstart and design page titles (TypeScript, Python, Java, Go, Ruby, PHP, .NET)

All proper nouns (TypeScript, Python, Java, Go, Ruby, PHP, Swift, .NET, OAuth, Maven Central, PyPI, npm, NuGet, RubyGems, Packagist, MCP, README) were preserved in their original casing.

Review & Testing Checklist for Human

• Verify proper noun preservation: Spot-check that acronyms like "API", "SDK", "MCP" are correctly capitalized throughout. In particular, check if "Multiple API definitions" in capabilities.mdx should be "Multiple API definitions" or "Multiple API Definitions" (API is an acronym).
• Check navigation display: Verify that the navigation sidebar and table of contents display correctly with the updated page titles on the preview deployment.
• Run Vale style checker: If Vale is available in your environment, run it against the changed files to catch any style guide violations that weren't caught (Vale was not available in the Devin environment).
• Visual consistency check: Preview 2-3 pages (e.g., TypeScript quickstart, capabilities overview) on the staging site to ensure headings look correct and consistent.

Notes

• All changes are text-only (no structural or functional changes)
• 23 files modified across guides, language overviews, and capabilities pages
• Navigation titles in sdks.yml were already in sentence case, so no changes were needed there

Link to Devin run: https://app.devin.ai/sessions/4e13998f25c14e809c3f979033c595ab
Requested by: Devin Logan (@devalog)