Add minimal Cooklang parser with first tests

- Create Roux.Parser with parseCookFile (splits paragraphs, treats
  each as a plain-text step, no metadata parsing yet)
- Add emptyMetadata to Roux.Types for convenience
- Add test dependencies: hspec, tasty-golden, tasty-hspec
- Add ParserSpec with 4 tests covering single step, multiple steps,
  empty input, and whitespace trimming
- Wire ParserSpec into test runner via tasty-hspec

package.yaml

@@ -60,6 +60,9 @@ tests:
     main: Spec.hs
     source-dirs: test
     dependencies:
+      - hspec
       - roux-server
       - tasty
+      - tasty-golden
+      - tasty-hspec
       - tasty-hunit