fix(auth): resolve demo login redirect loop, fix backend API bugs, restore clean login UI, and add comprehensive API docs with headers

src/app/login/page.tsx

@@ -30,22 +30,32 @@ export default function LoginPage() {
 
       if (data.success) {
         if (typeof window !== "undefined") {
-          localStorage.setItem("activeUserId", data.token)
+          // Set auth_token cookie required by Next.js 16 proxy.ts middleware
+          const cookieVal = data.role === "admin" ? "admin" : (data.token || "authenticated");
+          document.cookie = `auth_token=${cookieVal}; path=/; max-age=2592000; SameSite=Lax`;
+
+          localStorage.setItem("activeUserId", data.token);
           // Create new session token for single-device login
           const sessionToken = crypto.randomUUID();
           localStorage.setItem("active_session_token", sessionToken);
           
-          fetch(`/api/users/${data.token}/session`, {
-            method: 'POST',
-            headers: { 'Content-Type': 'application/json' },
-            body: JSON.stringify({ session_token: sessionToken })
-          }).finally(() => {
-            if (data.role === "admin") {
-              window.location.href = "/admin";
-            } else {
-              window.location.href = "/dashboard";
+          if (data.token && data.token !== "admin") {
+            try {
+              await fetch(`/api/users/${data.token}/session`, {
+                method: 'POST',
+                headers: { 'Content-Type': 'application/json' },
+                body: JSON.stringify({ session_token: sessionToken })
+              });
+            } catch (e) {
+              console.warn("Session update skipped", e);
             }
-          });
+          }
+
+          if (data.role === "admin") {
+            window.location.href = "/admin";
+          } else {
+            window.location.href = "/dashboard";
+          }
         }
       } else {
         setError(data.error || "Invalid email or password.")
@@ -54,6 +64,7 @@ export default function LoginPage() {
       setError("An error occurred. Please try again.")
     }
   }
+
   return (
     <div className="min-h-screen bg-background flex flex-col items-center justify-center p-6 selection:bg-[#00F0FF]/20">
       <Link href="/" className="absolute top-8 left-8 text-muted-foreground hover:text-foreground flex items-center gap-2 transition-colors font-medium">