fix: add static file serving with custom middleware

- Replaced wai-app-static with lightweight inline static file server
- Static files served from frontend/static/ under /static/ path
- Fixed ByteString/FilePath type mismatches for GHC 9.10
- Verified: CSS, manifest, login, signup, dashboard all HTTP 200

src/Sis/Page/Activity.hs

@@ -1,5 +1,13 @@
+{-# LANGUAGE DeriveAnyClass #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE UndecidableInstances #-}
 {-# OPTIONS_GHC -Wno-unused-imports -Wno-unused-do-bind -Wno-name-shadowing -Wno-redundant-constraints  -Wno-redundant-constraints #-}
-{-# LANGUAGE FlexibleContexts, DeriveAnyClass, DeriveGeneric, MultiParamTypeClasses, FlexibleInstances, UndecidableInstances, TypeApplications, TypeOperators, OverloadedStrings #-}
 
 module Sis.Page.Activity (page) where