feat: add LoginHandler component for executing login actions

- Created LoginHandler component to process /login command results
- Handles three action types:
  - add-account: Adds account to AccountManager and sets as active
  - error: Shows error toast with descriptive message
  - open-dialog: Shows info toast (dialog UI coming in next phase)
- Uses sonner for toast notifications with success/error feedback
- Integrated with WindowRenderer routing system
- Component auto-executes action on mount via useEffect

Files:
- src/components/LoginHandler.tsx (new)
- src/components/WindowRenderer.tsx (updated)

src/components/LoginHandler.tsx

@@ -0,0 +1,95 @@
+import { useEffect } from "react";
+import { toast } from "sonner";
+import { Check, X, Info } from "lucide-react";
+import type { ReadOnlyAccount } from "@/lib/account-types";
+import accountManager from "@/services/accounts";
+
+interface LoginHandlerProps {
+  action: "add-account" | "error" | "open-dialog";
+  account?: ReadOnlyAccount;
+  message?: string;
+}
+
+/**
+ * LoginHandler - Executes login command actions
+ *
+ * This component handles the result of the /login command:
+ * - add-account: Adds account to AccountManager and sets as active
+ * - error: Shows error toast
+ * - open-dialog: Shows info about opening login dialog (UI coming soon)
+ */
+export default function LoginHandler({
+  action,
+  account,
+  message,
+}: LoginHandlerProps) {
+  useEffect(() => {
+    const handleAction = async () => {
+      switch (action) {
+        case "add-account":
+          if (!account) {
+            toast.error("Failed to add account", {
+              description: "No account provided",
+              icon: <X className="h-4 w-4" />,
+            });
+            return;
+          }
+
+          try {
+            // Add account to manager
+            accountManager.addAccount(account);
+
+            // Set as active account
+            accountManager.setActive(account.id);
+
+            // Show success toast
+            toast.success("Account added successfully", {
+              description: `Logged in as ${account.pubkey.slice(0, 8)}...${account.pubkey.slice(-8)}`,
+              icon: <Check className="h-4 w-4" />,
+            });
+          } catch (error) {
+            toast.error("Failed to add account", {
+              description:
+                error instanceof Error ? error.message : "Unknown error",
+              icon: <X className="h-4 w-4" />,
+            });
+          }
+          break;
+
+        case "error":
+          toast.error("Login failed", {
+            description: message || "Unknown error occurred",
+            icon: <X className="h-4 w-4" />,
+          });
+          break;
+
+        case "open-dialog":
+          toast.info("Login dialog", {
+            description:
+              "Login dialog UI coming soon. For now, use: login <npub|nip-05|hex|nprofile>",
+            icon: <Info className="h-4 w-4" />,
+            duration: 5000,
+          });
+          break;
+
+        default:
+          toast.error("Unknown action", {
+            description: `Unhandled action: ${action}`,
+            icon: <X className="h-4 w-4" />,
+          });
+      }
+    };
+
+    handleAction();
+  }, [action, account, message]);
+
+  // This component doesn't render anything visible - it just executes the action
+  return (
+    <div className="flex items-center justify-center h-full w-full p-8">
+      <div className="text-center text-muted-foreground space-y-2">
+        <p className="text-sm">Processing login...</p>
+        <p className="text-xs">This window can be closed.</p>
+      </div>
+    </div>
+  );
+}

src/components/WindowRenderer.tsx

@@ -33,6 +33,7 @@ const SpellsViewer = lazy(() =>
 const SpellbooksViewer = lazy(() =>
   import("./SpellbooksViewer").then((m) => ({ default: m.SpellbooksViewer })),
 );
+const LoginHandler = lazy(() => import("./LoginHandler"));
 
 // Loading fallback component
 function ViewerLoading() {
@@ -175,6 +176,15 @@ export function WindowRenderer({ window, onClose }: WindowRendererProps) {
       case "spellbooks":
         content = <SpellbooksViewer />;
         break;
+      case "login-handler":
+        content = (
+          <LoginHandler
+            action={window.props.action}
+            account={window.props.account}
+            message={window.props.message}
+          />
+        );
+        break;
       default:
         content = (
           <div className="p-4 text-muted-foreground">