feat: add automatic re-authentication with MFA support

Implement automatic token refresh using stored credentials and TOTP MFA secret. When an API call fails with a 401/unauthorized error, the system now transparently re-authenticates using MONARCH_EMAIL, MONARCH_PASSWORD, and MONARCH_MFA_SECRET, then retries the original request.

Changes:
- Add refresh_authentication() function in auth.py for credential-based login
- Create @retry_on_auth_error decorator to handle and retry failed auth calls
- Apply decorator to all MCP tools (get_accounts, get_transactions, etc.)
- Add MONARCH_MFA_SECRET to .env.example with documentation
- Update login_setup.py to instruct users about required env vars
- Replace PROBLEM.md with PLAN.md documenting the implementation

login_setup.py

@@ -5,7 +5,6 @@ Saves session securely and provides the token for Docker environment.
 """
 
 import asyncio
-import os
 import getpass
 import sys
 from pathlib import Path
@@ -53,6 +52,21 @@ async def main():
             # Also save to local keyring for convenience
             save_token(token)
             print("\n✅ Token also saved to local system keyring.")
+
+            print("\n" + "=" * 50)
+            print("📝 IMPORTANT: For automatic re-authentication")
+            print("=" * 50)
+            print("\nIf you have MFA enabled on your Monarch account,")
+            print("add your MONARCH_MFA_SECRET to your .env file:")
+            print("\n  MONARCH_MFA_SECRET=your_totp_secret_here")
+            print("\nYou should have saved this secret when you first")
+            print("set up Google Authenticator/Authy for Monarch Money.")
+            print("\nThis allows the MCP server to automatically re-authenticate")
+            print("when your token expires.")
+            print("\nYou also need to add your credentials:")
+            print("  MONARCH_EMAIL=your_email@example.com")
+            print("  MONARCH_PASSWORD=your_password")
+            print("=" * 50)
         else:
             print("❌ Failed to retrieve token from MonarchMoney instance.")