data: add Confidence by Spotify startup credits

[nrk8286]

Closes #655

What changed

Adds Confidence by Spotify as one new vendor with exactly one startup offer: up to $75,000 in product credits for approved early-stage startups. The record also captures the published Growth capabilities, expanded controls, audit-log retention, unlimited surfaces, support, public contact route, and vendor-discretion eligibility.

Source

• https://confidence.spotify.com/pricing

Validation

• Pinned Sourcey Catalog Verifier: {"status":"valid","vendors":1,"programs":1,"offers":1}
• Data-only change: exactly vendors/co/confidence-by-spotify.yaml
• DCO sign-off included

Certification

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