Add Requesty startup program

[shawnruan0218-code]

What changed

• Add the missing Requesty vendor record.
• Capture the $1,000 AI credit and six-month platform-access startup bundle.
• Model the published partner-affiliation requirement.

Closes #611

Sources

• https://www.requesty.ai/startup

Validation

• Pinned Sourcey Catalog Verifier: {"status":"valid","vendors":1,"programs":1,"offers":1}

Certification

• I changed only allowed repository content and did not mix vendor YAML with other paths.
• Public sources substantiate every submitted factual value; any Sourcey-written prose is a neutral summary, not a fabricated vendor quote.
• I did not author verification, provenance, freshness, or signature claims.
• My commits include a Signed-off-by line.