docs: events now optional — Status headers + conditional HTML rendering

- ADR-015: Status → Optional with scaffold command + behavior note (bus absent
  means no-op, IJobQueue unaffected)
- events-and-jobs.md: prerequisite callout block explaining core-events is
  optional, how to scaffold, and which features require it
- data-flow-explainer.html: note bus is optional in BindProductionContext blurb;
  add inline comment in code snippet that bus is scaffoldable

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

docs/decisions/adr-015-events-and-jobs.md

@@ -1,6 +1,11 @@
 # ADR-015 — Cross-feature events and background jobs
 
-**Status:** Accepted
+**Status:** Optional — scaffold via `pnpm turbo gen core-package events`.
+When absent, `ctx.bus` is undefined and feature binders' `bus?.subscribe/publish`
+calls are silent no-ops. Cross-feature event fanout does not operate until
+core-events is scaffolded. `IJobQueue` (in `@repo/core-shared/jobs`) and the
+`gen event`/`gen job` generators remain fully functional without core-events.
+
 **Date:** 2026-05-08
 **Spec:** docs/superpowers/specs/2026-05-08-events-and-jobs-design.md
 **Plan:** docs/superpowers/plans/2026-05-08-events-and-jobs.md