data: add Keygraph Community Program

[hoangziet]

What changed

Adds one new vendor YAML for Keygraph and one startup offer under its publicly named Community Program. The offer records full Keygraph Pro at $0 in cloud-service fees for eligible seed and pre-Series-A startups with up to 20 Active Developers, including BYOK costs, graduation terms, and the application route.

Research and drafting were AI-assisted; the first-party sources and final YAML were checked against each other before submission.

Closes #747

Sources

• https://keygraph.io/community-program
• https://keygraph.io/terms

Validation

• Pinned Sourcey Catalog Verifier: {"status":"valid","vendors":1,"programs":1,"offers":1}
• Commit includes DCO sign-off.

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.