Extract Cooklang types into Data.CookLang module

- Create src/Data/CookLang.hs with all recipe types (Recipe, Section,
  StepItem, Ingredient, Cookware, Timer, RecipeRef, Quantity, Duration,
  Metadata, emptyMetadata)
- Data.CookLang has zero Roux imports — can be extracted to its own
  package
- Roux.Types now just re-exports from Data.CookLang
- Update all Roux.* modules and tests to import Data.CookLang directly
- All 30 tests passing, hlint clean

src/Roux/Html.hs

@@ -29,7 +29,7 @@ import Text.Blaze.Html5 as H
 import Text.Blaze.Html5.Attributes as A
 
 import qualified Roux.RecipeIndex as Idx
-import Roux.Types
+import Data.CookLang
 
 -- ---------------------------------------------------------------------------
 -- Sort mode for the index page