Add HuntAPI startup program

[kkmm6657]

What changed

Added HuntAPI and its publicly available Hunt for Startups offer. Eligible companies can receive up to 50% off the Premium or Startup plan for 12 months, along with priority support and developer resources.

Closes #642.

Sources

• https://www.huntapi.com/startup-program
• https://www.huntapi.com/pricing

Validation

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

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.