Phase 5: ship the catalog ActiveAdmin resources from the engine

- the 7 catalog admin files (softwares, releases, external_links,
  platform_links, images, files page, downloads) move to the engine's
  app/admin; the host ActiveAdmin instance loads them via
  ActiveAdmin.application.load_paths (single admin, URLs unchanged)
- engine initializers: Zeitwerk ignore for app/admin (production eager load)
  and load_paths + watchable_dirs registration, guarded by defined?(ActiveAdmin)
  so the admin-less dummy app boots
- images admin reads image owners from WarpEngine.config.image_owners; the
  host registers the Member owner in config/initializers/warp_engine.rb;
  the interim ImageUsage registry is gone
- fix: SoftwareImage.distinct.pluck clashed with its order(:position)
  default scope on MySQL (unscope(:order)) — introduced in phase 0, caught
  by the first authenticated /admin/images smoke test
- files page: download links use the public /file/ URL instead of the raw
  container path; the picker's stored path comes from config

Verified: both suites green, zeitwerk:check (production) clean, JSON
baselines intact, authenticated admin smoke test on every page incl.
the 3-level nested software form and Files picker mode.

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

apps/api/config/initializers/image_usage.rb

@@ -1,9 +0,0 @@
-# TTG-specifikus image-használók regisztrációja. to_prepare: reload után is újrafut.
-Rails.application.config.to_prepare do
-  ImageUsage.reset!
-  ImageUsage.register(
-    label: "member",
-    image_ids: -> { Member.where.not(image_id: nil).distinct.pluck(:image_id) },
-    usage_label: ->(image) { "member" if Member.where(image_id: image.id).exists? }
-  )
-end

apps/api/config/initializers/warp_engine.rb

@@ -0,0 +1,13 @@
+# WarpEngine host-konfiguráció. to_prepare: reload után is újrafut, ezért
+# értékadás (nem <<), hogy idempotens legyen.
+Rails.application.config.to_prepare do
+  WarpEngine.configure do |c|
+    c.image_owners = [
+      {
+        label: "member",
+        image_ids: -> { Member.where.not(image_id: nil).distinct.pluck(:image_id) },
+        usage_label: ->(image) { "member" if Member.where(image_id: image.id).exists? }
+      }
+    ]
+  end
+end