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>

packages/core-shared/src/di/bind-context.ts

@@ -8,7 +8,7 @@ import type {
 } from "./bind-protocols";
 
 /** Always-present fields. Feature binders rely on these unconditionally. */
-export type BindContextBase = {
+type BindContextBase = {
   tracer: ITracer;
   logger: ILogger;
 };