Add hello world to quickstart page

[mintlify-development]

Added hello world greeting text to the top of quickstart.mdx. Text appears after the frontmatter and before the main content as a simple test addition.

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Note

Low Risk
Single documentation text addition with no code or behavioral impact.

Overview
Adds a hello world greeting line near the top of quickstart.mdx (after frontmatter) as a simple content insertion/test.

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Test placeholder text committed to production documentation

Medium Severity

The text hello world appears to be test/placeholder content that was accidentally included for production. The PR description explicitly mentions this is "a simple test addition," which suggests it was meant for testing purposes rather than actual documentation content. This would make the quickstart page look unprofessional if deployed.