Add enum startup cloud credits

[yl124915300-dot]

What changed

Adds enum and its enum for Startups offer: up to €100,000 in cloud credits over 12 months for eligible EU-headquartered startups and scaleups that are ready for production workloads.

Closes #1250.

Sources

• https://enum.co/startups

Certification

• I changed only allowed repository content and did not mix Entity 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.

Local preflight with the repository's pinned Sourcey verifier passed for 1 entity, 1 program, and 1 offer with zero diagnostics.