Add think-cell startup program

[shawnruan0218-code]

What changed

• Add the missing think-cell vendor record.
• Capture the 90% first-year and 50% second-year startup discounts.
• Model the published age, employee-count, website, customer, and consultancy restrictions.

Closes #613

Sources

• https://www.think-cell.com/en/order/startup-program

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.