data: add Productlane Early Stage program

[Ezequiel-GH]

What changed

Adds a new Productlane vendor record with its Early Stage program and one structured Scale-plan discount offer.

Why

Productlane publishes a current startup-specific offer with explicit pricing, discount percentages, seat limits, eligibility, application access, and first-party documentation. The record closes #571.

Impact

After admission and merge, Sourcey can publish the Productlane Early Stage offer in the catalog with canonical vendor-owned sources.

Validation

• Parsed the YAML locally.
• Confirmed the description and summaries are within repository limits.
• Ran the exact digest-pinned Sourcey Catalog Verifier: {"status":"valid","vendors":1,"programs":1,"offers":1}.
• Commit includes a matching DCO sign-off.

[auscaster]

Thanks for this. sourcey/validation is green, but the evidence pass for this head could not locate support for every submitted fact, so sourcey/admission cannot go green yet.

Uncovered on the record: /summary, /economics.

Fix it on this same branch: either cite a public page that states the fact (add the URL to sources and reference its source_id from the record that needs it), or change the record to what the cited pages do say. Push to the branch and the checks re-run automatically.