docs: standardize voice, tone, and casing across prose pages

[mintlify]

Summary

Apply consistent sentence-case headings, second-person voice, active voice, and fix small grammar/typo issues across human-authored prose pages.

Changes

• Convert Title Case → sentence case for Card/Tab/Accordion titles and ### headings in overview.mdx, important-resources.mdx, support.mdx, tools-and-libraries.mdx, developer-guidelines.mdx, enterprise-api/activity/introduction.mdx, enterprise-api/activity/quickstart.mdx, enterprise-api/webhooks/quickstart.mdx.
• Rewrite a passive/third-person sentence in developer-terms.mdx and livestreams.mdx to second person + active voice.
• Tighten passive/awkward intros in enterprise-api/account-activity/introduction.mdx and x-ads-api/introduction.mdx.
• Fix typos and grammar: credentiails → credentials (basic-auth), recommended → recommend and broken markdown link (oauth-1-0a/overview), applications name → application + a X → an X (pin-based-oauth), the their → their (faq), a n App only → an App-only and Auth Flow → Auth flow (application-only), Login → Log in (bearer-tokens), Delegators → Delegator's (oauth-echo).
• Fix duplicate ## Quick navigation heading in x-api/fundamentals/data-dictionary.mdx.

Context

Style audit triggered by the initial docs import. Predominant style across the docs is sentence-case headings, second-person voice, and active voice — these edits bring older auth and enterprise pages in line.

[mintlify]

Preview deployment for your docs. Learn more about Mintlify Previews.

Project	Status	Preview	Updated (UTC)
x-corp	🟢 Ready	View Preview	Jun 9, 2026, 11:43 PM

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}