Add Tree Ring Memory product note

[TerminallyLazy]

Summary

• Add Tree Ring Memory as a sourced product note with a compact archive snapshot.
• Update product counts, product landscape, product architecture maps, discovery log, and Ymem relevance index.
• Keep claims bounded to official repo / press kit / GitHub metadata; no benchmark or MCP-server claim is added.

Validation

• git diff --check passed.
• Product-note count checked at 39 and archive count checked at 38.
• New product/archive frontmatter parsed with Ruby YAML.
• Tree Ring repo, site, and press kit returned HTTP 200.
• Duplicate PR/issue/code search for Tree Ring returned no existing entry.

Not run

• ruby scripts/verify_memory_refresh.rb in my sparse checkout because the local sparse clone intentionally omitted the papers/PDF archive and the verifier expects papers/index.md plus archive-count inputs.