Phase 6: polish — apipie matcher, install generator, engine migrations, docs

- host apipie matcher now globs the engine controllers, so /api/docs and
  /api/swagger keep documenting the catalog endpoints
- rails g warp_engine:install: initializer template + a clean
  create_warp_engine_tables migration (signed bigint PKs) for new hosts;
  TTG never runs it
- engine append_migrations initializer: future catalog migrations in the
  engine's db/migrate run via the host's rails db:migrate
- README documents the updater contract, config surface, host expectations
  (admin JS picker, apipie matcher) and the soft-delete/resurrection behavior
- make api-test runs both suites plus a production zeitwerk:check

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

apps/api/config/initializers/apipie.rb

@@ -4,8 +4,7 @@ Apipie.configure do |config|
   config.doc_base_url = "/api/docs"
   config.api_controllers_matcher = [
     "#{Rails.root}/app/controllers/api/**/*.rb",
-    "#{Rails.root}/app/controllers/update_controller.rb",
-    "#{Rails.root}/app/controllers/files_controller.rb"
+    "#{WarpEngine::Engine.root}/app/controllers/**/*.rb"
   ]
   config.validate = false
   config.translate = false