data: add PayPal for Startups offer

[luizguilhermetatsch]

What changed

Adds one new vendor record for the Sourcey startup-credits catalog:

PayPal — vendors/pa/paypal.yaml

• New vendor (slug: paypal), new program (paypal-for-startups), new offer (paypal-startup-fee-waiver).
• The offer: qualified US startups that are venture-capital backed (seed or Series A) get a waiver of PayPal Checkout and domestic PayPal Credit Card Processing fees for the first 12 months from their first live transaction.
• Eligibility: US resident, 18+, US PayPal business account in good standing, new PayPal customer (no prior Checkout/CC processing), must add PayPal Checkout and process at least one live transaction within 6 months of accepting the offer.
• Source: https://www.paypal.com/us/business/startups

Verification

Validated locally against the digest-pinned Sourcey Candidate Verifier
(sourcey-candidate-verifier.js validate-change) with the pinned taxonomy:

• Individual run (base f74092c → head a986b06): {"status":"valid","vendors":1,"programs":1,"offers":1}

Certification

• I changed only allowed repository content and did not mix vendor YAML with other paths.
• I did not author verification, provenance, freshness, or signature claims.
• My commits include a Signed-off-by line.