Phase 3: move service layer, serializers and DTOs into WarpEngine + dummy-app test suite

- all catalog services (update/software/highlighted/builds/file/file-manager/
  download/image + SoftwareResponseBuilder), the SoftwareUpdater platform
  services and their concerns, Blueprinter serializers (incl. TimestampFields)
  and the 4 DTOs now live in the engine under WarpEngine::
- constantize dispatch strings use absolute names
  (WarpEngine::SoftwareUpdater::<Platform>Service)
- container paths read from WarpEngine.config everywhere (FileService,
  DownloadService, FileManagerService, ArchiveExtraction, ReleaseSerializer
  path rewriting); FileManagerService base path is now lazy
- engine requires blueprinter itself; gemspec declares blueprinter + rubyzip
- engine test suite: spec/dummy app (mysql warp_engine_test, catalog-only
  schema), rails_helper with engine-local factories; catalog model/service
  specs and factories moved from the host
- host suite keeps TTG specs and loads catalog factories from the engine

Verified: engine suite 40 green, host suite 14 green, /api/software and
/api/builds byte-identical to baselines, admin OK.

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

spec/dummy/config/application.rb

@@ -0,0 +1,23 @@
+require_relative "boot"
+
+require "rails"
+require "active_model/railtie"
+require "active_record/railtie"
+require "action_controller/railtie"
+require "action_view/railtie"
+require "action_dispatch/railtie"
+
+Bundler.require(*Rails.groups)
+require "warp_engine"
+
+module Dummy
+  class Application < Rails::Application
+    config.load_defaults 8.0
+    config.eager_load = false
+
+    config.time_zone = "UTC"
+    config.active_record.default_timezone = :utc
+
+    config.hosts.clear
+  end
+end