Add BMAD framework, authentication, and new features

keep-notes/app/actions/auth.ts

@@ -0,0 +1,29 @@
+'use server';
+
+import { signIn } from '@/auth';
+import { AuthError } from 'next-auth';
+
+export async function authenticate(
+  prevState: string | undefined,
+  formData: FormData,
+) {
+  try {
+    await signIn('credentials', formData);
+  } catch (error) {
+    if (error instanceof AuthError) {
+      console.error('AuthError details:', error.type, error.message);
+      switch (error.type) {
+        case 'CredentialsSignin':
+          return 'Invalid credentials.';
+        default:
+          return `Auth error: ${error.type}`;
+      }
+    }
+    // IMPORTANT: Next.js redirects throw a special error that must be rethrown
+    if (error instanceof Error && error.message === 'NEXT_REDIRECT') {
+      throw error;
+    }
+    console.error('Non-AuthError during signin:', error);
+    throw error;
+  }
+}