Web server with recipe index page

- Add Roux.Server: WAI application using wai+warp directly
  - Scans .cook files from recipe directory on startup
  - GET / → HTML index page listing all recipes
  - Other routes → 404
- Add Roux.RecipeIndex: directory scanning and recipe parsing
  - scanRecipes: lists .cook files, parses each, extracts titles
  - Falls back to filename when metadata title is absent
- Add Roux.Html: blaze-html rendering with Pico CSS
  - indexPage: renders recipe list with links
  - urlEncode: percent-encodes filenames for URLs
- Update Roux.hs: re-exports Server.app and Types
- Add filepath to dependencies

src/Roux/Server.hs

@@ -0,0 +1,63 @@
+{- | WAI application for the Roux recipe server.
+
+Handles HTTP requests directly via wai — no framework.  Currently serves
+a single index page listing all discovered recipes.
+-}
+module Roux.Server (
+    app,
+) where
+
+import Control.Monad (when)
+import Data.ByteString.Lazy (ByteString)
+import qualified Network.HTTP.Types as HTTP
+import qualified Network.Wai as Wai
+
+import qualified Roux.Html as Html
+import qualified Roux.RecipeIndex as Idx
+
+{- | Build the WAI 'Application' given a path to the recipe directory.
+
+Recipes are scanned once at startup.  A future improvement could watch
+the directory for changes and rebuild the index.
+-}
+app :: FilePath -> IO Wai.Application
+app recipeDir = do
+    putStrLn $ "[roux] scanning recipes from " <> recipeDir
+    recipes <- Idx.scanRecipes recipeDir
+    let count = length recipes
+        ok = length [() | r <- recipes, isRight (Idx.riRecipe r)]
+        errs = count - ok
+    putStrLn $ "[roux] found " <> show count <> " recipe(s)"
+    when (errs > 0) $
+        putStrLn $
+            "[roux] " <> show errs <> " had parse errors"
+    -- Return the application; recipes are captured in the closure.
+    pure (handleRequest recipes)
+
+-- | Route an incoming request to the appropriate handler.
+handleRequest :: [Idx.RecipeInfo] -> Wai.Application
+handleRequest recipes request respond =
+    case Wai.pathInfo request of
+        [] -> respond (htmlResponse (Html.indexPage recipes))
+        _ -> respond notFound
+
+-- | Build a 200 HTML response.
+htmlResponse :: ByteString -> Wai.Response
+htmlResponse body =
+    Wai.responseLBS
+        HTTP.status200
+        [("Content-Type", "text/html; charset=utf-8")]
+        body
+
+-- | 404 response.
+notFound :: Wai.Response
+notFound =
+    Wai.responseLBS
+        HTTP.status404
+        [("Content-Type", "text/plain")]
+        "Not found"
+
+-- | Check if an 'Either' is 'Right'.
+isRight :: Either a b -> Bool
+isRight (Right _) = True
+isRight (Left _) = False