fix: address Phase 1 code-quality review findings

- Generator feature templates emit ctx-arg signatures + updated checklist
- signUpUseCase test for bus=undefined path
- di-explainer.html: bind-dev-seed no-arg → ctx
- data-flow-explainer.html: tradeoff card → ctx
- BindContextBase no longer exported
- CLAUDE.md binder bullet: drop vestigial cast guidance

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/architecture/data-flow-explainer.html

@@ -2209,7 +2209,7 @@ 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;()</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 (post-Plan-9).</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>