Improve authentication flow for improved user experience

Update Replica HTML to prompt user for sign-in if not authenticated, and handle authentication errors more gracefully.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 01ad339d-418c-47f5-be76-423bcdc9b50c
Replit-Commit-Checkpoint-Type: intermediate_checkpoint
Replit-Commit-Event-Id: dd13dc49-9b6b-4bde-a7ac-b7c67625f68c
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/c6a48625-afd1-4b8b-b95e-595805001e6c/01ad339d-418c-47f5-be76-423bcdc9b50c/fCtRmKG
Replit-Helium-Checkpoint-Created: true

replica/index.html

@@ -487,13 +487,18 @@
                 try {
                     const isSignedIn = await puter.auth.isSignedIn();
                     if (!isSignedIn) {
-                        // For anonymous use, Puter.js can sometimes work without sign-in for certain models
-                        // but most AI features require an account. 
-                        // We'll proceed if they are already signed in, or try to sign in.
-                        console.log("User not signed in to Puter");
+                        addChatMessage('ai', "I need you to sign in with Puter to access AI capabilities.");
+                        await puter.auth.signIn();
+                        // Re-check after sign in
+                        if (!await puter.auth.isSignedIn()) {
+                            addChatMessage('ai', "Authentication failed. Please try again.");
+                            return;
+                        }
                     }
                 } catch (e) {
                     console.error("Puter Auth Error:", e);
+                    addChatMessage('ai', "Authentication failed. Please try again.");
+                    return;
                 }
             }