spike: adopt the install generator's shim wiring

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: planetaska

spike/app/javascript/controllers/hibiki_controller.js

@@ -0,0 +1,7 @@
+// Registers the packaged hibiki client (the "hibiki-rails" module: the
+// engine's importmap pin, or the npm package in bundler apps) as the
+// "hibiki" Stimulus controller — the Ruby helpers hardcode that
+// identifier in data-controller. File-backed on purpose: `bin/rails
+// stimulus:manifest:update` re-derives this exact registration from the
+// filename, so it survives manifest rewrites.
+export { default } from "hibiki-rails"

spike/app/javascript/controllers/index.js

@@ -2,9 +2,6 @@
 import { application } from "controllers/application"
 import { eagerLoadControllersFrom } from "@hotwired/stimulus-loading"
 eagerLoadControllersFrom("controllers", application)
-
-// The packaged hibiki client (vendored by the hibiki_rails engine, pinned
-// as "hibiki-rails"). The identifier must be "hibiki" — the Ruby helpers
-// hardcode it in data-controller.
-import HibikiController from "hibiki-rails"
-application.register("hibiki", HibikiController)
+// The packaged hibiki client is registered by the eager-loaded
+// hibiki_controller.js shim (file-backed so stimulus:manifest:update
+// can't drop it).