Blank screen shown when user has no todos

[niat-web]

Bug Report

What happened:
When a brand new user logs in for the first time
and has zero todos, the todo list section appears
completely blank with no message or guidance.

Expected behavior:
Show a friendly empty state with:

• An icon (like a checkmark or clipboard)
• Message: "You have no todos yet!"
• Sub message: "Click '+ Add Todo' to get started"

Steps to reproduce:

1. Create a brand new account
2. Login
3. See blank todo list with no guidance

Why this is important:
New users are confused about what to do next.
A good empty state guides them to take action.

Suggested fix:
Add empty state component in TodoPage.jsx
that shows when todos array is empty.