Update README with VPG logo

[ismaeltocruz]

Adding VPG to top of README

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Note

Low Risk
Low risk documentation-only change; no code, behavior, or runtime dependencies are affected.

Overview
Adds a centered Digital Public Goods badge (linked to digitalpublicgoods.net) to the top of README.md, along with a short quoted verification statement.

^{Written by Cursor Bugbot for commit 32a1089. This will update automatically on new commits. Configure here.}

[emmaeturner]

README update looks good. CI is failing in Lint & self tests (1 failed in dbt self-tests), which appears unrelated to the README change.

[ismaeltocruz]

This PR only changes documentation.
CI failures appear to be pre-existing on main (all recent Actions runs are failing).
The failure is due to duplicate scenario_id values in self-test SQL (MISSING-1), unrelated to this change.