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>

app/admin/downloads.rb

@@ -0,0 +1,106 @@
+ActiveAdmin.register WarpEngine::Download, as: "Download" do
+  actions :index, :show
+
+  menu priority: 7, label: "📊 Download Stats"
+
+  scope :all, default: true
+  scope("Today")         { |scope| scope.where("downloads.created_at >= ?", Date.current.beginning_of_day) }
+  scope("This week")     { |scope| scope.where("downloads.created_at >= ?", 1.week.ago) }
+  scope("This month")    { |scope| scope.where("downloads.created_at >= ?", 1.month.ago) }
+  scope("With release")    { |scope| scope.where.not(release_id: nil) }
+  scope("Without release") { |scope| scope.where(release_id: nil) }
+
+  config.sort_order = "created_at_desc"
+
+  sidebar "Summary", only: :index do
+    dl style: "display:grid;grid-template-columns:1fr auto;gap:6px 12px;margin:0;" do
+      dt { strong "Total" }
+      dd { b WarpEngine::Download.count.to_s }
+
+      dt { strong "Today" }
+      dd { b WarpEngine::Download.where("created_at >= ?", Date.current.beginning_of_day).count.to_s }
+
+      dt { strong "This week" }
+      dd { b WarpEngine::Download.where("created_at >= ?", 1.week.ago).count.to_s }
+
+      dt { strong "This month" }
+      dd { b WarpEngine::Download.where("created_at >= ?", 1.month.ago).count.to_s }
+    end
+  end
+
+  sidebar "Top 10 Files", only: :index do
+    table_for WarpEngine::Download.group(:file_path)
+                      .select("file_path, COUNT(*) as dl_count, MAX(created_at) as last_dl")
+                      .order("dl_count DESC")
+                      .limit(10) do
+      column("File") { |row| span row.file_path.split("/").last, style: "font-family:monospace;font-size:11px;" }
+      column("DL") { |row| row.dl_count }
+    end
+  end
+
+  sidebar "Top 5 Software", only: :index do
+    rows = WarpEngine::Download.joins(release: :software)
+                   .group("softwares.title")
+                   .order("count_all DESC")
+                   .limit(5)
+                   .count
+    if rows.any?
+      table_for rows do
+        column("Software") { |title, _| title }
+        column("DL") { |_, count| count }
+      end
+    else
+      para "No data", style: "color:#999;font-style:italic;"
+    end
+  end
+
+  index do
+    id_column
+    column(:file_path) { |d| span d.file_path.truncate(50), style: "font-family:monospace;font-size:12px;" }
+    column("Software") { |d| d.release&.software ? link_to(d.release.software.title, admin_software_path(d.release.software)) : "–" }
+    column("Release")  { |d| d.release&.version || "–" }
+    column :ip_address
+    column("User-Agent") { |d| d.user_agent&.truncate(40) }
+    column("Referer")    { |d| d.referer&.truncate(40) }
+    column :created_at
+  end
+
+  filter :file_path_cont, label: "File path"
+  filter :release_software_title_cont, label: "Software"
+  filter :ip_address_cont, label: "IP address"
+  filter :user_agent_cont, label: "User-Agent"
+  filter :referer_cont, label: "Referer"
+  filter :created_at
+
+  show do
+    attributes_table do
+      row :id
+      row(:file_path) { |d| span d.file_path, style: "font-family:monospace;" }
+      row("Software") do |d|
+        if d.release&.software
+          link_to d.release.software.title, admin_software_path(d.release.software)
+        else
+          "–"
+        end
+      end
+      row("Release") do |d|
+        if d.release
+          link_to d.release.version, admin_software_release_path(d.release.software, d.release)
+        else
+          "–"
+        end
+      end
+      row :ip_address
+      row :user_agent
+      row :referer
+      row :created_at
+      row :updated_at
+    end
+  end
+
+  controller do
+    def scoped_collection
+      super.includes(release: :software)
+    end
+  end
+end