Phase 1: warp_engine gem skeleton (path gem, mounted engine)

- libs/ruby/warp_engine: gemspec, WarpEngine::Engine (isolate_namespace with
  empty table_name_prefix), WarpEngine.configure surface (container paths,
  update_secret, image_owners), empty engine routes
- host Gemfile: path gem; host routes: mount WarpEngine::Engine => "/" as
  the last entry so host routes always win
- docker: api build context moved to repo root so libs/ is visible at
  bundle-install time; ./libs:/libs runtime mount; root .dockerignore to keep
  data/ and node_modules out of the build context

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

apps/api/Gemfile

@@ -1,6 +1,10 @@
 source "https://rubygems.org"
 
 gem "rails", "~> 8.0"
+
+# Katalógus-engine. A relatív path hoston (apps/api -> repo-gyökér/libs) és a
+# konténerben (/app -> /libs mount) is ugyanoda oldódik fel.
+gem "warp_engine", path: "../../libs/ruby/warp_engine"
 gem "mysql2", "~> 0.5"
 gem "puma", ">= 5.0"
 gem "rubyzip", "~> 2.3"