fix(routes): root path "/" now routes to LandingAction

StaticPagesController parseRoute' used endOfInput for "/", but IHP passes
the raw path string so the parser received "/" not "". Match it explicitly
with string "/" before endOfInput, consistent with all other routes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Web/Routes.hs

@@ -304,7 +304,7 @@ instance AutoRoute SessionsController
 -- WP-0015 — Public intro / tutorial pages (manual routing so / is the root)
 instance CanRoute StaticPagesController where
     parseRoute' = choice
-        [ do endOfInput; pure LandingAction
+        [ do _ <- string "/"; endOfInput; pure LandingAction
         , do _ <- string "/capabilities"; endOfInput; pure CapabilitiesAction
         , do _ <- string "/tutorial"; endOfInput; pure TutorialAction
         , do _ <- string "/extension-guide"; endOfInput; pure ExtensionGuideAction