[AS-289] Cross-link Solutions toolboxes in README

[ilan-bel]

Summary

Adds the same "Apollo Solutions toolboxes — where this fits" matrix to all four Solutions toolbox repos so a reader landing in any one can find the right tool for their need. This is the cross-link minimum from AS-289 — a lower-risk alternative to consolidating the repos.

The matrix lives near the top of each README and highlights the current repo's row. The four repos covered:

• apollosolutions/pse-toolbox — drop-in utilities
• apollosolutions/reference-architecture — end-to-end working supergraph
• apollosolutions/supergraph-template-with-router — minimal starter template
• apollosolutions/graphos-feature-template — narrow feature demo template

Companion PRs are open against the three other repos with identical changes.

Test plan

• Each repo's README renders the table cleanly on github.com
• The current repo's row is the only one marked (you are here)
• All four apollosolutions/* links resolve

🤖 Generated with Claude Code

[apollo-solutions-reviewer]

The cross-link matrix is a clean, consistent approach and satisfies the AS-289 intent for the three live repos: each README gets the same comparison table, the current repo's row is correctly marked (you are here), and the pse-toolbox / reference-architecture / graphos-feature-template links and descriptions are accurate. CI is green (CLA signed, secrets scan passed).

One blocking issue, on the supergraph-template-with-router row. That repo is both archived (read-only) and private. Two problems follow:

1. The intro text states these are "four overlapping public repos," but supergraph-template-with-router is private; the link will 404 for customers and most external readers, which directly undercuts the customer-discoverability goal in the ticket.
2. The row presents it as a recommended live starter ("Pick 'Use this template' in GitHub to fork it"), but an archived repo cannot be used as a template or accept forks via that flow. AS-289's acceptance criteria call for retired repos to be pointed to as a fallback, not promoted as a primary choice.

This is the same matrix shipped identically in the companion PRs (pse-toolbox #23, graphos-feature-template #12), so the fix needs to land in all three. Recommended resolution, matching the ticket comment's open question: either unarchive and make the repo public before linking it as a live option, or drop the "Use this template" guidance and reframe it as an archived/reference-only entry (or remove the row). Once the supergraph-template-with-router row is corrected, this is good to merge.

Minor: the intro's "four overlapping public repos" wording will be inaccurate as long as one of the four is private; adjust the count or wording alongside the fix above.

[apollo-solutions-reviewer]

Re-reviewed at 3b67088. Both blocking items from the prior review are addressed. The intro now says "three public toolbox repos" and the matrix lists only the three live, public repos (reference-architecture, pse-toolbox, graphos-feature-template), with this repo's row correctly marked (you are here). The archived-and-private supergraph-template-with-router is no longer promoted as a live starter; it now lives in a callout that states external readers cannot access it and "Use this template" no longer works, and it directs readers to graphos-feature-template as the closest live equivalent. That matches the AS-289 intent of pointing to retired repos as a fallback rather than a primary choice. CI is green. Approving. Note: companion PRs pse-toolbox #23 and graphos-feature-template #12 carry the same change and should land the same reframing; they are out of scope for this review.