feat: add Supabase startup credit offer

[idrisawad]

Add Supabase for Startups / Launch program:

• 00+ platform credits
• 6 months free Pro plan (5/mo)
• Eligibility: <M funding, <3 years, <10 employees

Source: supabase.com/solutions/startups

What changed

Describe the vendor or offer facts changed by this pull request.

Sources

List the first-party URLs supporting the change.

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.

[auscaster]

Closing: this adds the same entity as the earlier open #845, which holds it. The first open pull request for an entity is the one reviewed, so this copy cannot go further. To help, review or improve #845 instead.