Add basic login screen with form-based authentication

Adds /login route with HTML template that handles GET (show form) and
POST (authenticate). On successful login, sets session cookie and
redirects to /. Also adds framework support for redirects and cookies
in route handlers.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

express/routes.ts

@@ -25,7 +25,9 @@ const okText = (result: string): Result => {
 
 const routes: Route[] = [
     ...authRoutes,
+    basicRoutes.home,
     basicRoutes.hello,
+    basicRoutes.login,
     {
         path: "/slow",
         methods: ["GET"],