Closes the last two staleness threads from the docs audit:
1. data-flow-explainer.html had four "Plan-9" / "post-Plan-9"
references in the masthead, lede, fix-up bullet, and bindDevSeed
blurb. Stripped — the architecture is now just "vertical-feature".
No content changes beyond the noun rename.
2. audit-and-compliance-explainer.html had a footer link to
../superpowers/specs/2026-05-11-audit-and-compliance-design.md
(archived to .archive/ earlier). Replaced with a link to
ADR-018, which is the durable design record.
3. data-flow-explainer.html + di-explainer.html were inter-linked
with audit + conformance explainers, but had no markdown entry
point — they were orphans from any guide or architecture doc.
architecture/overview.md gains a new "Interactive explainers"
section listing all four single-file HTML walkthroughs with one
sentence each, so they're discoverable from the documented
entry point. The four pages already cross-link to each other.
Final state (verified by repo-wide grep): zero "Plan-N" / "Phase-N"
/ "docs/superpowers/" references in docs/ (excluding .archive/ which
is gitignored). Legitimate `superpowers:brainstorming` skill refs
in agent-first-workflow-and-conformance.md are preserved — those
reference an external plugin, not a repo path.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>