Phase 4: Recipe references + all 4 example file validation

- Fix pRecipeRef to include ./ prefix in stored path
- Add recipe reference test
- Add parse-validation tests for all 4 example .cook files
  (EasyPancakes, FriedRice, CoffeeSouffle, OlivierSalad)
- All 24 tests passing, all examples parse without error

src/Roux/Parser.hs

@@ -131,11 +131,12 @@ pLineBreak = do
 pRecipeRef :: Parser StepItem
 pRecipeRef = do
     _ <- P.char '@'
+    -- Consume @ and store ./ as part of the path
     _ <- P.char '.'
     _ <- P.char '/'
     path <- P.many (P.noneOf "{(\n\\")
     mqty <- P.optionMaybe (P.between (P.char '{') (P.char '}') pQuantityBody)
-    return (StepRecipeRef (RecipeRef path (join mqty)))
+    return (StepRecipeRef (RecipeRef ("./" <> path) (join mqty)))
 
 -- | Ingredient: @name{quantity%unit}(preparation)
 pIngredient :: Parser StepItem