Add Swarmia startup offer

[offer-catalog-worker]

What changed

Adds Swarmia and its startup-specific offer: 50% off Standard or Enterprise annual plans for the first year.

Closes #800

Sources

• https://www.swarmia.com/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.