docs: expand CLAUDE.md with page types, widgets, lint, and source refs

[Nesmeshnoy]

Summary

Captures the rules another agent and I established while rebuilding the docs into reproducible guidance for future agents working in this repo.

• Page types — Pillar vs Reference vs Compliance. What each must / must not include, where things live (api-reference/operations/* vs interop-apis/* vs compliance/*).
• Source code map — smartbox / interop / prior-auth private repos for agent reference, plus their public Docker Hub images that are OK to link from docs.
• Aidbox docs as style and platform reference, with explicit note that docs.aidbox.app cannot be hyperlinked (the absolute-links lint blocks it).
• Widgets — block vs self-closing shapes, explicit nesting rules (tab → tabs, step → stepper, swagger-* → swagger).
• Swagger widget family — already supported by docs-tools but previously undocumented in CLAUDE.md.
• Lint additions — dead-end-pages (warning, with exemption rules) and absolute-links default domains made explicit.

No changes to docs/* content — this is meta-documentation for whoever (human or agent) writes Payerbox docs next.

Test plan

• bun lint passes (15 checks, only pre-existing warnings on docs/* from the in-flight rebuild)
• Review readability of the new sections
• Confirm the private-repo / public-image split is the policy we want documented