docs(architecture): strip Plan-9/superpowers refs from HTML + wire orphan explainers

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>

docs/architecture/audit-and-compliance-explainer.html

@@ -1517,7 +1517,7 @@ footer .colophon {
       <a href="vertical-feature-spec.md">vertical-feature-spec.md</a>
       <a href="overview.md">overview.md</a>
       <a href="dependency-flow.md">dependency-flow.md</a>
-      <a href="../superpowers/specs/2026-05-11-audit-and-compliance-design.md">2026-05-11 · audit design spec</a>
+      <a href="../decisions/adr-018-audit-and-compliance.md">ADR-018 · audit &amp; compliance</a>
     </div>
     <div>
       <h5>Guide</h5>

docs/architecture/data-flow-explainer.html

@@ -1476,12 +1476,12 @@ footer .colophon {
 <header class="masthead frame">
   <div class="folio-row">
     <span class="folio-label"><span class="folio-mark"></span> template-vertical / architecture / explainer</span>
-    <span>2026-05-06 · post-Plan-9</span>
+    <span>2026-05-06</span>
   </div>
 
   <div class="title-block">
     <h1 class="title">A guided tour<br>of one feature's<br><em>data flow</em>.</h1>
-    <p class="lede">An internal explainer for the post-Plan-9 architecture — written for the engineer who built it and just wants the mental model in one place. Click through the request flow, flip the DI binding mode, swap features. Real code from this repo, not a tutorial.</p>
+    <p class="lede">An internal explainer for the vertical-feature architecture — written for the engineer who built it and just wants the mental model in one place. Click through the request flow, flip the DI binding mode, swap features. Real code from this repo, not a tutorial.</p>
   </div>
 
   <div class="contents-row">
@@ -2003,7 +2003,7 @@ footer .colophon {
           <li>Per-feature ownership — auth's errors don't leak into blog</li>
         </ul></div>
         <div class="cons"><h5>Cons</h5><ul>
-          <li>Every constructor must set <code>this.name</code> (R6) — easy to forget, was the systemic Plan-9 fix-up</li>
+          <li>Every constructor must set <code>this.name</code> — easy to forget, and the cause of opaque error names when omitted</li>
           <li><code>InputParseError</code> is duplicated per feature (~6 lines × 5) — by design, but feels redundant</li>
           <li>Adding a new error class = update the feature's <code>procedures.ts</code> map too</li>
         </ul></div>
@@ -2210,7 +2210,7 @@ footer .colophon {
     <div class="tradeoff-card">
       <div class="tag">di/bind-dev-seed.ts</div>
       <h3>Dev-seed binder</h3>
-      <p class="blurb"><code>bindDevSeed&lt;F&gt;(ctx: BindContext)</code> — unbinds the empty mock, rebinds a populated mock (post-Plan-9).</p>
+      <p class="blurb"><code>bindDevSeed&lt;F&gt;(ctx: BindContext)</code> — unbinds the empty mock, rebinds a populated mock.</p>
       <div class="pc-cols">
         <div class="pros"><h5>Pros</h5><ul>
           <li>Dev mode shows realistic data without Payload running — design review, storybook, offline work all just work</li>

docs/architecture/overview.md

@@ -133,3 +133,14 @@ Each feature owns its own InversifyJS `Container` + symbol table. No shared symb
 ## Spec reference
 
 `docs/architecture/vertical-feature-spec.md` is the canonical design.
+
+## Interactive explainers
+
+Four single-file HTML walkthroughs sit alongside this overview. They're self-contained (no build step) and best viewed locally in a browser.
+
+- [`data-flow-explainer.html`](./data-flow-explainer.html) — request and event flow through one feature, with the DI binding mode toggle and feature swap controls.
+- [`di-explainer.html`](./di-explainer.html) — the full container + symbols + binder lifecycle.
+- [`feature-conformance-explainer.html`](./feature-conformance-explainer.html) — companion to ADR-020-adjacent conformance design (also linked from `agent-first-workflow-and-conformance.md` and `runbook.md`).
+- [`audit-and-compliance-explainer.html`](./audit-and-compliance-explainer.html) — companion to ADR-018 (also linked from `dependency-flow.md` and `guides/audit-and-compliance.md`).
+
+The four pages cross-link to each other; entering any of them surfaces the others.