Add SPA static file serving from backend

Backend (Server.hs):
- serveStaticOrSpa: serves static files from --static-dir
- SPA fallback: extensionless paths serve index.html
- MIME type mapping for html/css/js/png/svg/ico/woff2

Frontend:
- ES module imports with import map for Mithril CDN
- Build script: tsc + copy index.html + static assets

CLI:
- --static-dir flag (default: frontend/dist)
- scripts/run passes through extra args
- Dockerfile CMD points at /usr/local/share/sis/static

app/Main.hs

@@ -2,7 +2,7 @@
 
 {- | Entry point for the Sis chore tracker server.
 
-Starts a Warp HTTP server and serves the JSON API.
+Starts a Warp HTTP server, serves the JSON API and the SPA frontend.
 -}
 module Main (main) where
 
@@ -14,6 +14,7 @@ import Sis.Server qualified as Sis
 
 data Options = Options
   { optPort :: Int
+  , optStaticDir :: FilePath
   }
 
 optionsParser :: Opt.Parser Options
@@ -28,26 +29,36 @@ optionsParser =
           <> Opt.value 8080
           <> Opt.showDefault
       )
+    <*> Opt.strOption
+      ( Opt.long "static-dir"
+          <> Opt.metavar "DIR"
+          <> Opt.help "Directory containing the SPA frontend static files"
+          <> Opt.value "frontend/dist"
+          <> Opt.showDefault
+      )
 
 main :: IO ()
 main = do
-  opts <- Opt.execParser $
-    Opt.info (optionsParser Opt.<**> Opt.helper) $
-      Opt.fullDesc
-        <> Opt.progDesc "Sis — shared household chore tracker"
-        <> Opt.header "sis-server"
+  opts <-
+    Opt.execParser $
+      Opt.info (optionsParser Opt.<**> Opt.helper) $
+        Opt.fullDesc
+          <> Opt.progDesc "Sis — shared household chore tracker"
+          <> Opt.header "sis-server"
 
   -- Install a SIGTERM handler so Docker stop works cleanly.
-  _ <- Signals.installHandler
-    Signals.sigTERM
-    (Signals.Catch (putStrLn "[sis] shutting down"))
-    Nothing
+  _ <-
+    Signals.installHandler
+      Signals.sigTERM
+      (Signals.Catch (putStrLn "[sis] shutting down"))
+      Nothing
 
-  let waiApp = Sis.app
+  let waiApp = Sis.app (optStaticDir opts)
 
   let settings =
-        Warp.setPort (optPort opts)
-          $ Warp.setBeforeMainLoop (putStrLn $ "[sis] listening on port " ++ show (optPort opts))
-          Warp.defaultSettings
+        Warp.setPort (optPort opts) $
+          Warp.setBeforeMainLoop
+            (putStrLn $ "[sis] listening on port " ++ show (optPort opts))
+            Warp.defaultSettings
 
   Warp.runSettings settings waiApp