Update architecture diagram

[fricklerhandwerk]

We changed a few things since it was merged, and it's also syntactically broken (bold and italics need to be syntactically correct).

• Evaluation doesn't currently touch the Nix store
• Evaluation ingests into PG
• CVE ingestion triggers matching, not some generic worker
• Would be super cool to have links to the code that does the work named in a given box (make sure lychee checks those too!)

https://github.com/NixOS/nix-security-tracker/blob/main/docs/architecture.mermaid