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/Html.hs

@@ -0,0 +1,55 @@
+{- | HTML rendering for the Roux web interface.
+
+Uses blaze-html directly.  Styling via Pico CSS (inlined in the page).
+-}
+module Roux.Html (
+    indexPage,
+) where
+
+import Data.ByteString.Lazy (ByteString)
+import Data.Text (Text)
+import qualified Data.Text as T
+import qualified Text.Blaze.Html.Renderer.Utf8 as R
+import Text.Blaze.Html5 as H
+import Text.Blaze.Html5.Attributes as A
+
+import qualified Roux.RecipeIndex as Idx
+
+-- | Render the recipe index page.
+indexPage :: [Idx.RecipeInfo] -> ByteString
+indexPage recipes =
+    R.renderHtml $
+        H.docTypeHtml $ do
+            H.head $ do
+                H.meta ! A.charset "utf-8"
+                H.meta ! A.name "viewport" ! A.content "width=device-width, initial-scale=1"
+                H.title "Roux — Recipes"
+                H.link ! A.rel "stylesheet" ! A.href "https://cdn.jsdelivr.net/npm/@picocss/pico@2/css/pico.min.css"
+            H.body $ do
+                H.main ! A.class_ "container" $ do
+                    H.h1 "Roux"
+                    H.p "Your personal recipe collection."
+                    H.h2 "Recipes"
+                    H.ul $ mapM_ recipeItem recipes
+
+-- | Render a single recipe list item.
+recipeItem :: Idx.RecipeInfo -> Html
+recipeItem info =
+    H.li $ case Idx.riRecipe info of
+        Left _err ->
+            H.span ! A.class_ "error" $ do
+                H.toHtml (Idx.riTitle info)
+                " (parse error)"
+        Right _recipe ->
+            H.a ! A.href (H.toValue ("/recipes/" <> urlEncode (Idx.riFilename info))) $
+                H.toHtml (Idx.riTitle info)
+
+-- | Percent-encode a filename for use in a URL path segment.
+urlEncode :: FilePath -> Text
+urlEncode = T.pack . concatMap encodeChar
+  where
+    encodeChar c
+        | c == ' ' = "%20"
+        | c == '#' = "%23"
+        | c == '%' = "%25"
+        | otherwise = [c]