Add Obseria startup offer

[offer-catalog-worker]

What changed

Adds Obseria and its startup-specific offer: 50% off an annual plan for the first year.

Closes #799

Sources

• https://obseria.io/en/pricing/startup/

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]

Thank you for this contribution, and apologies for the slow review.

The record itself is structurally sound and sourcey/validation is green. I am holding it rather than merging it, because obseria.io currently sits below the threshold this repository uses for automatic admission of a new entity (Domain Rating 0). That threshold is about the entity's public footprint, not about the quality of your submission.

I am leaving this pull request open. It needs a human admission decision rather than a change from you, so there is nothing to fix on your side right now. If the entity has published sources I have missed that establish it more strongly, please add them here and I will take another look.

_{Reviewed by hand against CONTRIBUTING.md and the canonical-source rule, 28 Aug 2026.}