data: add Contextual AI Google Scale perk

[nwinkelman2]

Summary

• add Contextual AI as an AI/ML platform entity
• record Google Cloud's current Scale Tier-exclusive $1,500 Contextual AI credit perk
• model Google Cloud as the membership access operator and preserve the Scale-only eligibility boundary

Closes #1244

First-party evidence

• Contextual AI product/domain: https://contextual.ai/
• Google Cloud Startup Perks economics and exclusivity: https://cloud.google.com/startup/perks
• Google Scale-member redemption form: https://docs.google.com/forms/d/1YYqh23ulfT_Rx2ftcGm4M6Xtxgau42D1yb4iUyEPtbc/viewform

The Google page states that starred perks are exclusive to Scale Tier members and lists $1.5K in Contextual AI credits + expert support. The redemption form separately confirms current Scale Tier membership is required and includes Contextual AI among the selectable exclusive perks.

Verification

• exact Sourcey candidate verifier: passed (1 entity, 0 programs, 1 offer)
• live parent release: sha256:f54ae5559bef1aae2cdbacb1c26d5860eeb4459221b4469e67117cc1d09a01b8
• identity-context digest: sha256:e6d084ac433cdd820f9cd7219a06aa3c3a77811e5b555d87e743350684129425
• git diff --check origin/main...HEAD: passed
• DCO sign-off: present