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>

app/dtos/warp_engine/file_result_dto.rb

@@ -0,0 +1,15 @@
+module WarpEngine
+  class FileResultDto
+    attr_reader :type, :path, :url
+
+    def initialize(type:, path: nil, url: nil)
+      @type = type
+      @path = path
+      @url  = url
+    end
+
+    def self.file(path)    = new(type: :file,      path: path)
+    def self.redirect(url) = new(type: :redirect,  url: url)
+    def self.not_found     = new(type: :not_found)
+  end
+end

app/dtos/warp_engine/file_show_input_dto.rb

@@ -0,0 +1,3 @@
+module WarpEngine
+  FileShowInputDto = Struct.new(:path, keyword_init: true)
+end

app/dtos/warp_engine/image_show_input_dto.rb

@@ -0,0 +1,3 @@
+module WarpEngine
+  ImageShowInputDto = Struct.new(:id, keyword_init: true)
+end

app/dtos/warp_engine/update_input_dto.rb

@@ -0,0 +1,7 @@
+module WarpEngine
+  UpdateInputDto = Struct.new(:platform, :name, :version, keyword_init: true) do
+    def initialize(platform:, name:, version: nil)
+      super
+    end
+  end
+end