fix: address Phase 1 spec review findings

- di-explainer.html: update stale JS data strings from positional-arg
  form (bindAllProduction(config), bindProductionBlog(config,tracer,...))
  to ctx-arg form (bindAllProduction(deps), bindProductionBlog(ctx)) with
  a note on ctx shape.
- auth/sign-up.use-case: change bus param from IEventBus to
  EventBusProtocol|undefined; guard bus.publish with if(bus) so the use
  case is safe when core-events is absent (Phase 3+).
- auth/bind-production + bind-dev-seed: drop as IEventBus cast and unused
  IEventBus import; ctx.bus is now passed directly (typed as
  EventBusProtocol|undefined).
- marketing-pages/bind-production + bind-dev-seed: drop as IJobQueue cast
  and unused IJobQueue import; wrap event-handler DI block in if(queue)
  guard so the handler is only bound when core-jobs is wired.
- core-shared/src/index.ts: add `export * from "./di"` as the plan
  specified (subpath export alone is no longer the only access path).

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

packages/core-shared/src/index.ts

@@ -1,3 +1,4 @@
 export { requireEnv } from "./lib/env";
 export { toIsoString } from "./lib/date";
+export * from "./di";
 export * from "./instrumentation/index";